Anti-backlash optical fiber laser

Abstract

The application discloses an anti-return light type optical fiber laser and relates to the technical field of optical fiber lasers, and comprises a gain optical fiber with a signal light center wavelength, wherein the maximum absorption cross section of the gain optical fiber is in the range of 0.5-1.5 pm, and the minimum emission cross section is 0.5-1.5 pm; the wavelength 976 nm is set as lambda 1, the wavelength 1030 nm is set as lambda 2, the absorption cross section of the gain optical fiber at lambda 1 is set as sigma (lambda 1), the emission cross section of the gain optical fiber at lambda 2 is set as sigma (lambda 2), the absorption cross section of the gain optical fiber at lambda 1 is set as sigma (lambda 1), and the emission cross section of the gain optical fiber at lambda 2 is set as sigma (lambda 2); the gain optical fiber simultaneously satisfies the following cross section constraint relationship: sigma (lambda 1) / sigma (lambda 2) >= 1.5 and sigma (lambda 2) / sigma (lambda 1) <= 0.5. The application limits the size constraint relationship between the absorption cross section and the emission cross section of the gain optical fiber at each wavelength, so that the gain optical fiber has a low enough absorption cross section and a high enough emission cross section at the signal light wavelength, the reabsorption loss of the laser to the signal light is reduced, and the amplification spontaneous emission and the parasitic oscillation of the 1030 nm waveband are effectively inhibited.

Description

Technical Field

[0001] This invention relates to the field of fiber laser technology, and specifically to an anti-backlight fiber laser. Background Technology

[0002] Fiber lasers use rare-earth-doped fiber as the gain medium and generate stimulated emission amplification through pump light excitation. They are characterized by compact structure, high electro-optic efficiency, and excellent beam quality, and are widely used in materials processing, communications, and scientific research. However, with the continuous breakthroughs in high-power fiber laser technology and the increasing demand for higher efficiency, better beam quality, and more compact systems, high-brightness pumping technology has become a key bottleneck for further improving system performance.

[0003] Studies have shown that the insufficient brightness of semiconductor pump sources makes it difficult to meet the requirements of ultra-high power output in single-fiber lasers. To address this issue, in-band pumping technology has become a key approach. In-band pumping is a highly efficient pumping method applied to ytterbium-doped fiber lasers and amplifiers. Its core principle is to use a pump source with a wavelength close to that of the signal light, thereby reducing quantum loss and thermal effects. However, in practical applications, the reflected light generated by the subsequent amplifier can flow back into the resonant cavity of the preceding laser. Even if the reflected light power is low, it can lead to a significant decrease in the output power of the preceding laser, and may even cause spectral instability and device damage, severely restricting system reliability.

[0004] Regarding the aforementioned backlight interference problem, the degree to which different gain fibers are affected by backlight varies. Conventional gain fibers, while possessing high gain at the signal wavelength, still retain some residual gain in the 1080nm band. When backlight is injected into the resonant cavity in the reverse direction, it is easily amplified and causes power fluctuations. Therefore, how to improve the backlight resistance of fiber lasers at the gain medium level without adding additional optical isolation devices is a pressing technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an anti-backlight fiber laser. This laser can be used as a co-band pump source for a 1080nm fiber laser, effectively reducing backlight interference in this application scenario and achieving stable signal power output. It features a compact structure and stable reliability.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an anti-backlight fiber laser, comprising: A pump source, a gain fiber, a high-reflection grating, a low-reflection grating, and a cladding power stripper are sequentially fused together to form a forward-pumped linear resonant optical path. The gain fiber has a signal light center wavelength. The The coverage area is 1008nm±10nm, in The maximum absorption cross section of the gain fiber within the specified range is Minimum launch cross-section is ; The center wavelength of the laser output from the pump source, 976 nm, is defined as the reference wavelength. The gain fiber in The absorption cross section at that location is ; With the peak wavelength of the gain fiber's emission cross-section being 1030 nm as... The gain fiber in The launch cross section at that location is ; The gain fiber simultaneously satisfies the following cross-sectional constraint relationship: ,and .

[0007] Furthermore, the gain fiber is a ytterbium-doped silica double-clad fiber, and the core of the gain fiber is doped with Yb. 3+ ion.

[0008] Furthermore, the absorption cross section The emission cross section was calculated using Beer-Lambert's law. It was obtained using McCumber's theory.

[0009] Furthermore, the core diameter of the gain fiber is 15μm to 25μm, the cladding diameter of the gain fiber is 100μm to 150μm, and the numerical aperture of the core of the gain fiber is 0.05 to 0.07.

[0010] Furthermore, the pump source is a semiconductor laser, and the center wavelength of the output laser of the pump source is 976±10nm.

[0011] Furthermore, the center wavelength of the high-reflectivity grating is Reflectivity ≥ 99%, and with The 3dB bandwidth of the center wavelength is ≥2nm.

[0012] Furthermore, the center wavelength of the low-reflectivity grating is The reflectivity is 5%–10%, and it is mainly based on... The 3dB bandwidth of the center wavelength is ≥1nm.

[0013] Furthermore, the pump source output end is fused with the high-reflectivity grating input end to form a forward pumping structure.

[0014] Furthermore, the input end of the high-reflectivity grating is fused to the output end of the pump source, and the output end of the high-reflectivity grating is fused to one end of the gain fiber; the input end of the low-reflectivity grating is fused to the other end of the gain fiber, and the output end of the low-reflectivity grating is fused to the input end of the cladding power stripper.

[0015] Furthermore, the output end of the cladding power stripper serves as the laser output end.

[0016] The technical effects and advantages provided by the present invention in the above technical solution are as follows: 1. By constraining the size relationship between the absorption and emission cross sections of the gain fiber at each wavelength, the gain fiber simultaneously possesses a sufficiently low absorption cross section and a sufficiently high emission cross section at the signal light wavelength. This reduces the reabsorption loss of the laser on the signal light and effectively suppresses amplified spontaneous emission and parasitic oscillations in the 1030nm band. At the same time, the spectral selectivity of this gain fiber makes it difficult for the 1080nm backlight to be effectively amplified in the fiber, thereby improving the laser's output efficiency and anti-backlight performance in terms of gain fiber material selection. 2. This invention can achieve stable anti-backlight operation without the need for additional optical isolation devices, and has the advantages of compact structure and stable reliability. It is particularly suitable for high-power co-band pumped fiber laser systems. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0018] Figure 1 This is a schematic diagram of the basic structure of the present invention; Figure 2 The absorption and emission cross-section spectra of the gain fiber in Embodiment 1 of the present invention are shown. Figure 3 This is a comparison curve of the signal optical power changing with the injected return optical power in Embodiment 2 of the present invention; Figure 4 This is a schematic diagram of the structure of the amplifier used in the comparative experiment of the present invention; Figure 5 This is a graph showing the optical-to-optical conversion efficiency of the anti-reflection performance comparison experiment of the present invention.

[0019] Explanation of reference numerals in the attached figures: 1. Pump source; 2. High-reflection grating; 3. Low-reflection grating; 4. Gain fiber; 5. Cladding power stripper; 6. Laser amplifier. Detailed Implementation

[0020] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0021] This invention provides, for example Figures 1 to 5 The illustrated anti-reflection fiber laser includes: a pump source 1, a high-reflection grating 2, a low-reflection grating 3, a gain fiber 4, and a cladding power stripper 5.

[0022] It should be noted that the appendix Figure 4 and attached Figure 5 The "laser amplifier" mentioned is an external application device and is not part of the anti-backlight fiber laser of this invention. The laser of this invention is fused to an external 1080nm fiber amplifier via the output of the cladding power stripper 5, serving as its co-band pump source. The laser amplifier 6 only appears in the comparative experiment as an external device to verify the anti-backlight performance of this invention, used to simulate the impact of backlight generated by the subsequent amplifier on the laser of this invention in a real-world application scenario.

[0023] Example 1: As Figure 1 As shown, this embodiment provides an anti-backlight fiber laser, including: a pump source 1, a high-reflection grating 2, a low-reflection grating 3, a gain fiber 4, and a cladding power stripper 5. The pump source 1, high-reflection grating 2, gain fiber 4, low-reflection grating 3, and cladding power stripper 5 are sequentially fused together to form a forward-pumped linear resonant optical path.

[0024] In this embodiment, pump source 1 is a semiconductor laser with an output center wavelength of 976±10nm and a pump power of 400W. Its output pigtail is a passive double-clad fiber. The output end of pump source 1 is fused to the input end of high-reflectivity grating 2.

[0025] In this embodiment, the center wavelength of the high-reflectivity grating 2 Using 1008nm, reflectivity ≥99%, The 3dB bandwidth of the center wavelength is 2nm, and its output end is fused to the input end of the gain fiber 4.

[0026] In this embodiment, the center wavelength of the low-reflection grating 3 The wavelength is 1008 nm, and the reflectivity is 5%–10%, preferably 10%. With a 3dB bandwidth of 1nm at the center wavelength, its output is fused to the input of the cladding power stripper 5.

[0027] In this embodiment, the gain fiber 4 is a ytterbium-doped silica double-clad fiber with specific spectral characteristics. Its matrix material is silica glass, and the core is doped with Yb. 3+ Ions. Yb3+ The doping concentration is designed based on the 976nm pump absorption requirements. The absorption coefficient of the gain fiber used in this embodiment is 33dB / m at 976nm. The core diameter of the gain fiber 4 is 20μm, the cladding diameter is 130μm, the core numerical aperture is 0.06, and the length is 1-3m, preferably 2m. The output end of the gain fiber 4 is fused to the input end of the low-reflection grating 3.

[0028] In this embodiment, the absorption and emission cross-section spectra of the selected gain fiber are as follows: Figure 2 As shown.

[0029] Signal light center wavelength Use 1008nm; Measurements show that the gain fiber used in this embodiment meets the following requirements: ,and .

[0030] The above equations represent the specific measured parameters of the optical fiber in this embodiment, which satisfy the inequality constraints of the parameter relationship described in claim 1.

[0031] In this embodiment, the high-reflection grating 2, the low-reflection grating 3, and the gain fiber 4 together constitute a linear resonant cavity.

[0032] In this embodiment, the cladding power stripper 5 is connected to the output end of the low-reflection grating 3; the cladding power stripper 5 is a water-free cladding power stripper with a stripping efficiency ≥20dB; the output end of the cladding power stripper 5 outputs a signal laser.

[0033] The working principle of the anti-backlight fiber laser in this embodiment is as follows: The 976nm pump light output from pump source 1 is transmitted through a high-reflectivity grating 2 and enters a linear resonant cavity composed of the high-reflectivity grating 2, gain fiber 4, and low-reflectivity grating 3. The gain fiber 4 absorbs the 976nm pump light and generates stimulated emission. In this embodiment, the center wavelength of the signal light... The wavelength is set to 1008nm. After frequency selection and amplification by the resonant cavity composed of high-reflection grating 2 and low-reflection grating 3, the output laser has a center wavelength of 1008nm and is then output through the cladding power stripper 5.

[0034] In this process, because the gain fiber used in this embodiment satisfies and The parameter relationships are as follows. Lasers in the 1080nm band are difficult to amplify effectively within the resonant cavity, thus physically suppressing the generation of amplified spontaneous emission and parasitic oscillations, thereby improving the anti-backlight performance and operational stability of fiber lasers.

[0035] The fiber laser in this embodiment can be used as a co-band pump source for a 1080nm fiber amplifier. In practical applications, the reflected light generated at the back end of the 1080nm fiber laser propagates in the reverse direction along the optical path into the interior of the preceding fiber laser. During the propagation of the reflected light, the cladding power stripper 5 can strip away part of the reflected light in the cladding; simultaneously, the gain fiber 4 suppresses the gain amplification of the reflected light in the fiber core. The two work synergistically to suppress the reflected light from both the fiber core and cladding dimensions, thereby improving the fiber laser's anti-reflection capability.

[0036] Example 2: To verify the difference between the gain fiber of the present invention and other conventional gain fibers in terms of anti-backlight performance, based on the signal light wavelength range and gain fiber structure parameters disclosed in the present invention, a simulation model was established using the MATLAB simulation platform and the fiber laser rate equations, and the following simulation comparison verification was performed.

[0037] Simulation parameter settings: The center wavelength range of the signal light is defined as 1008±10nm in the claims and specification of this invention. In this embodiment, the center wavelength of the signal light is 1018nm, the pump light wavelength is 976nm, and the pump power is 400W. Regarding the grating parameters, the center wavelength is 1018nm for all gratings, the reflectivity of the low-reflection grating is 10%, and the reflectivity of the high-reflection grating is 99%.

[0038] Regarding the gain fiber parameters, the fiber length is 2m for both. Comparative simulations were conducted using the gain fiber of this invention (Scheme A) and a conventional gain fiber (Scheme B). Both fibers are ytterbium-doped silica fibers, with a core diameter of 20μm, a cladding diameter of 130μm, and a core numerical aperture of 0.06. The absorption coefficient of the gain fiber used in Scheme A is 33dB / m at 976nm, while the absorption coefficient of the conventional gain fiber used in Scheme B is 28dB / m at 976nm.

[0039] The absorption and emission cross sections of the gain fiber used in Scheme A satisfy the following: ,and ; The absorption and emission cross sections of the conventional gain fiber used in Scheme B satisfy the following: ,and .

[0040] As can be seen from the above parameters, the gain fiber used in Scheme A satisfies the parameter relationship defined in claim 1. However, the gain fiber used in scheme B does not satisfy this parameter relationship.

[0041] Except for the different types of gain fiber, the other device parameters and operating conditions remained consistent in the two sets of simulations.

[0042] All of the above parameters fall within the range of signal light wavelengths and structural parameters defined in the claims and specification of this invention, and no new technical features are introduced.

[0043] Simulation methods and results: In the simulation, a fixed amount of 1080nm laser light was set at one end of the low-reflection grating to simulate the effect of the 1080nm reflected light from the amplifier on the laser of this invention and a conventional gain fiber laser, and the decrease in signal light power was observed. The reflected light power was gradually increased from 0mW to 500mW, and the signal light output power at different reflected light powers was recorded. Figure 3 As shown, a comparison curve of the signal optical power changing with the injected return optical power is presented for the two schemes.

[0044] Simulation results show that as the reverse-injected return optical power gradually increases, the signal optical power under both gain fiber conditions decreases. However, at each return optical power point, the signal optical power decrease in scheme A is less than that in scheme B. Furthermore, at a return optical power of 500mW, scheme A experiences a power decrease of only 5.4W compared to no return optical power, while scheme B experiences a decrease of 11.2W. These results demonstrate that, compared to conventional gain fibers, the gain fiber of this invention exhibits superior anti-return optical performance at a signal wavelength of 1018nm, effectively suppressing the gain capability of return optical power within the fiber core and reducing the impact of return optical power on the signal optical power.

[0045] It should be noted that the parameters and results used in this simulation verification are only one specific implementation of the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0046] Comparison Experiment with Connected Amplifiers To verify the anti-backlight performance of the present invention, a comparative test was conducted using the anti-backlight fiber laser described in Example 1 (Scheme A) and a fiber laser constructed using a gain fiber that does not satisfy the parameter relationship of the present invention (Scheme B).

[0047] In this embodiment, The absorption and emission cross sections of the gain fiber used in Scheme A satisfy the following: ,and ; The absorption and emission cross sections of the gain fiber used in Scheme B satisfy the following: ,and .

[0048] As can be seen from the above parameters, the gain fiber used in Scheme A satisfies the parameter relationship defined in claim 1, while the gain fiber used in Scheme B does not satisfy this parameter relationship. Therefore, it is used as a comparative example to verify the effect of the parameter relationship described in this invention on improving the anti-backlight performance of fiber lasers.

[0049] Scheme A uses the gain fiber selected in this invention, with an absorption coefficient of 33 dB / m at 976 nm; Scheme B uses conventional gain fiber, with an absorption coefficient of 31.6 dB / m at 976 nm; both are 2 m long. Except for the gain fiber, all other structural parameters of Scheme A and Scheme B are identical. Before being connected to the amplifier, the laser output powers of Scheme A and Scheme B were measured to be 352 W and 348 W, respectively, and the center wavelength of the output laser was 1008 nm for both.

[0050] like Figure 4 As shown, schemes A and B were used as pump sources and connected to the same 1080nm fiber amplifier 6 with fixed parameters. The center operating wavelength of amplifier 6 was 1080nm, and the seed light power was 50W. The seed light power and other operating parameters remained constant in both tests. The amplifier output power was recorded after schemes A and B were connected, and the optical-to-optical conversion efficiency from 1008nm to 1080nm was calculated.

[0051] Optical-to-optical conversion efficiency is defined as the percentage of the total 1080nm output power of the amplifier, after deducting the fixed 50W seed light power, to the injected 1008nm pump light power.

[0052] Figure 5 The image shows the optical-to-optical conversion efficiency curves from the comparative experiment on the anti-backlight performance of this invention. The test results show that when using scheme A as the pump source, the amplifier's conversion efficiency is 80.2%; while when using scheme B as the pump source, the amplifier's conversion efficiency is 71.7%. Scheme A has a higher efficiency, indicating that under the same amplifier operating conditions, scheme A has better anti-backlight capability than scheme B. This is because 1080nm backlight is difficult to effectively amplify in the gain fiber, thus causing less interference to the pump source, allowing the pump light to be injected into the amplifier more efficiently and converted into 1080nm laser light.

[0053] The above comparative experiments show that by selecting gain fibers with specific spectral characteristics, the present invention effectively improves the anti-backlight capability of fiber lasers in co-band pumping applications.

[0054] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A fiber laser with anti-backlight capability, characterized in that, include: Pump source (1), gain fiber (4), high-reflection grating (2), low-reflection grating (3) and cladding power stripper (5) are sequentially spliced ​​to form a forward pumped linear resonant optical path. The gain fiber (4) has a signal light center wavelength. The The coverage area is 1008nm±10nm, in The maximum absorption cross section of the gain fiber (4) within the range is Minimum launch cross-section is ; The reference wavelength is defined as the center wavelength of the laser output from the pump source (1), which is 976 nm. The gain fiber (4) in The absorption cross section at that location is ; With the peak wavelength of the emission cross-section of the gain fiber (4) being 1030 nm as... The gain fiber (4) in The launch cross section at that location is ; The gain fiber (4) simultaneously satisfies the following cross-sectional constraint relationship: ,and .

2. The anti-backlight fiber laser according to claim 1, characterized in that: The gain fiber (4) is a ytterbium-doped silica double-clad fiber, and the core of the gain fiber (4) is doped with Yb. 3+ ion.

3. The anti-backlight fiber laser according to claim 1, characterized in that: The absorption cross section The emission cross section was calculated using Beer-Lambert's law. The results were obtained using McCumber theory.

4. The anti-backlight fiber laser according to claim 1, characterized in that: The core diameter of the gain fiber (4) is 15μm to 25μm, the cladding diameter of the gain fiber (4) is 100μm to 150μm, and the core numerical aperture of the gain fiber (4) is 0.05 to 0.

07.

5. The anti-backlight fiber laser according to claim 1, characterized in that: The pump source (1) is a semiconductor laser, and the center wavelength of the output laser of the pump source (1) is 976±10nm.

6. The anti-backlight fiber laser according to claim 1, characterized in that: The center wavelength of the high-reflectivity grating (2) is Reflectivity ≥ 99%, and with The 3dB bandwidth of the center wavelength is ≥2nm.

7. The anti-backlight fiber laser according to claim 1, characterized in that: The center wavelength of the low-reflectivity grating (3) is The reflectivity is 5%–10%, and it is mainly based on... The 3dB bandwidth of the center wavelength is ≥1nm.

8. The anti-backlight fiber laser according to claim 1, characterized in that: The output end of the pump source (1) is fused to the input end of the high-reflectivity grating (2) to form a forward pumping structure.

9. The anti-backlight fiber laser according to claim 1, characterized in that: The input end of the high-reflectivity grating (2) is fused to the output end of the pump source (1), and the output end of the high-reflectivity grating (2) is fused to one end of the gain fiber (4); the input end of the low-reflectivity grating (3) is fused to the other end of the gain fiber (4), and the output end of the low-reflectivity grating (3) is fused to the input end of the cladding power stripper (5).

10. The anti-backlight fiber laser according to claim 1, characterized in that: The output end of the cladding power stripper (5) serves as the laser output end.

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