Dual acousto-optic modulated single-frequency fiber laser and working method thereof

Abstract

The application belongs to the technical field of fiber lasers, and particularly relates to a double acousto-optic modulation single-frequency fiber laser and a working method thereof. A seed source is used for outputting laser; an acousto-optic external modulation module is used for externally modulating the laser according to a pulse signal with a set pulse width, so as to obtain a pulse laser signal; a fiber amplifier is used for amplifying the pulse laser signal, so as to obtain an amplified signal; an acousto-optic pulse pickup module is used for modulating the amplified signal according to the pulse signal with the set pulse width under different frequency division ratios, so as to obtain single-frequency pulse laser signals with different repetition frequencies; and a collimator is used for outputting the single-frequency pulse laser signals. Compared with the prior art, the application adopts external modulation, controls pulse width and repetition frequency through double acousto-optic modulators, breaks through the limitation of traditional internal modulation parameter coupling, and realizes stable output of 1030nm repetition frequency, pulse width high flexibility and customizable single-frequency laser.

Description

Technical Field

[0001] This invention belongs to the field of fiber laser technology, specifically relating to a dual acousto-optic modulated single-frequency fiber laser and its operating method. Background Technology

[0002] Single-frequency lasers possess advantages such as narrow linewidth, low noise, and long coherence length, leading to their widespread application in high-resolution spectroscopy, gravitational wave detection, and lidar. In particular, single-frequency lasers in the 1μm band (1030nm, 1064nm, etc.) have attracted significant attention due to their immense application potential in astronomy, the semiconductor industry, and biomedicine. The 1030nm single-frequency pulsed laser, with its narrow linewidth, high coherence, and flexible nonlinear frequency conversion capabilities, demonstrates irreplaceable application value in cutting-edge technologies, specifically including: The 515nm green light generated by frequency doubling is used in the biomedical field for early cancer fluorescence detection and precision processing of perovskite solar cells. The 343nm ultraviolet light generated by frequency tripling is used in the semiconductor industry to achieve 7nm node photoresist exposure and supports super-resolution microscopy to achieve 30nm resolution single-molecule imaging. The fundamental frequency light can drive Raman laser systems to achieve multi-wavelength output and is used for marine chlorophyll remote sensing and extreme ultraviolet light source research and development.

[0003] However, due to the strict requirements on the pulse width and repetition frequency of single-frequency lasers in certain specific applications, the development of single-frequency pulsed lasers with tunable repetition frequency and pulse width has become an urgent need.

[0004] Currently, most implementations of 1030nm pulsed single-frequency fiber lasers employ internal modulation. Internal modulation directly modulates the laser generation process by changing the laser's pump source parameters, such as current and voltage, thereby altering the laser's output characteristics (e.g., intensity and frequency). This modulation method directly affects the laser generation process, controlling the laser from its source. However, it has the following main drawbacks: (1) Limitations of laser performance by internal modulation: Traditional single-frequency lasers use internal modulation (directly control pump source parameters), resulting in low modulation rate (only supports low frequency), poor laser wavelength stability, and linewidth that is easily interfered with.

[0005] (2) The pulse parameter adjustment is not flexible enough. Existing technologies cannot achieve independent and wide-range adjustment of pulse repetition frequency and pulse width (such as fixed repetition frequency and non-adjustable pulse width), which cannot meet the diverse application needs.

[0006] (3) Fiber amplification noise leads to low signal-to-noise ratio. During fiber amplification, spontaneous emission (ASE) noise introduces continuous components, resulting in low signal-to-noise ratio (SNR < 50dB), which affects high-precision applications. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a single-frequency fiber laser with dual acousto-optic modulation and its operating method. It utilizes dual acousto-optic modulators for external modulation, with the dual acousto-optic modulators used to control the laser pulse width and repetition rate, breaking through the limitations of traditional internal modulation parameter coupling and achieving highly flexible customized output.

[0008] The technical solution adopted by this invention to solve its technical problem is as follows: A dual acousto-optic modulated single-frequency fiber laser, comprising: Seed source, used for laser output; An acousto-optic external modulation module includes a generator and a first acousto-optic modulator. The generator is used to output a pulse signal with a set pulse width, and the first acousto-optic modulator is used to externally modulate the laser according to the pulse signal with the set pulse width to obtain a pulsed laser signal. The fiber amplifier includes a first-stage single-mode fiber amplifier and a second-stage double-clad fiber amplifier, which are used to amplify the pulsed laser signal sequentially to obtain an amplified signal. An acousto-optic pulse pickup module includes a driver and a second acousto-optic modulator. The driver is used to set a frequency division ratio, and the second acousto-optic modulator is used to modulate the amplified signal according to the pulse signal with the set pulse width at different set frequency division ratios to obtain single-frequency pulse laser signals with different repetition frequencies. A collimator is used to output the single-frequency pulse laser signal.

[0009] Preferably, the first-stage single-mode fiber amplifier includes a single-mode continuous pump source, a wavelength division multiplexer, a single-mode ytterbium-doped gain fiber, and a first bandpass filter; the pulsed laser signal enters the single-mode ytterbium-doped gain fiber through the wavelength division multiplexer, is amplified under the pumping action of the single-mode continuous pump source, and then passes through the first bandpass filter to filter out the remaining pump light and spontaneous emission (ASE) components, thus obtaining a first-stage amplified pulsed laser signal.

[0010] Preferably, the single-mode continuous pump source adopts a forward pumping method and is a 976nm single-mode continuous pump source.

[0011] Preferably, the length of the single-mode ytterbium-doped gain fiber is 80 mm.

[0012] Preferably, the second-stage double-clad fiber amplifier includes a multimode continuous pump source, a combiner, a double-clad ytterbium-doped gain fiber, a cladding mode stripper, and a second bandpass filter. The first-stage amplified pulsed laser signal obtained by the first-stage single-mode fiber amplifier and the pump light emitted by the multimode continuous pump source enter the double-clad ytterbium-doped gain fiber through different ports of the combiner and are amplified again. Then, together with the remaining pump light, they pass through the cladding mode stripper, where the remaining pump light is stripped. The spontaneous emission (ASE) component is then filtered out by the second bandpass filter to obtain the second-stage amplified pulsed laser signal.

[0013] Preferably, the multimode continuous pump source adopts a forward pumping method and is a 976nm multimode continuous pump source; the length of the double-clad ytterbium-doped gain fiber is 100mm.

[0014] Preferably, the seed source is isolated from the first acousto-optic modulator by a first optical isolator; the single-mode ytterbium-doped gain fiber is isolated from the first bandpass filter by a second optical isolator; and the second bandpass filter is isolated from the acousto-optic pulse pickup module by a third optical isolator.

[0015] Preferably, the acousto-optic pulse pickup module further includes a coupler for outputting a reference signal light; the driver is also used to set a delay time, and the second acousto-optic modulator modulates the single-frequency pulse laser signal to synchronize it with the reference signal light pulse according to the set delay time and the reference signal light.

[0016] Preferably, the center wavelength of the output single-frequency pulsed laser is 1030nm, the repetition frequency is adjustable from 500Hz to 1kHz, the pulse width is adjustable from 10ns to 30ns, the output linewidth is less than 50kHz, the signal-to-noise ratio is greater than 50dB, and the long-term power fluctuation is less than 1%.

[0017] The operating method of the dual acousto-optic modulated single-frequency fiber laser of the present invention includes the following steps: Laser output from seed source; A pulse signal with a set pulse width is output by the generator, and the first acousto-optic modulator externally modulates the laser according to the pulse signal with the set pulse width to obtain a pulsed laser signal; The pulsed laser signal is amplified sequentially by a first-stage single-mode fiber amplifier and a second-stage double-clad fiber amplifier to obtain an amplified signal. The frequency division ratio is set by the driver, and the amplified signal is modulated by the second acousto-optic modulator according to the pulse signal with the set pulse width at different frequency division ratios to obtain single-frequency pulse laser signals with different repetition frequencies. The collimator outputs the single-frequency pulse laser signal.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention provides a single-frequency fiber laser with dual acousto-optic modulation and its operating method. It adopts external modulation and controls the pulse width and repetition rate through dual acousto-optic modulators respectively, breaking through the limitation of traditional internal modulation parameter coupling, and realizing stable output of single-frequency laser with 1030nm repetition rate, high pulse width flexibility and customizability.

[0019] 2. This invention introduces external modulation technology, which uses a first acousto-optic modulator to control the pulse width and a second acousto-optic modulator to control the repetition rate to independently regulate the laser characteristics, thereby avoiding interference with the laser generation process and ensuring wavelength stability and high-speed modulation.

[0020] 3. This invention utilizes dual acousto-optic modulators working in tandem. The first modulator sets the pulse width, while the second modulator adjusts the repetition frequency through the frequency division ratio, enabling independent parameter control and adapting to scenarios such as lidar and photolithography.

[0021] 4. This invention employs a two-stage bandpass filter to remove noise outside the 1029-1031nm range and an acousto-optic pulse pickup module to remove continuous ASE components, thereby improving the signal-to-noise ratio to >50dB, ensuring stable output power with fluctuations of <1%, and meeting the requirements for precision measurement.

[0022] In summary, this invention surpasses existing technologies in terms of parameter flexibility, noise suppression, and system stability, providing a customized, high signal-to-noise ratio, narrow linewidth 1030 nm single-frequency laser solution for high-precision lidar, lithography, and spectral analysis. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of a single-frequency fiber laser with dual acousto-optic modulation provided in Example 1.

[0024] Figure 2 The output pulse width diagram corresponding to the typical output parameter 1 provided in Example 1.

[0025] Figure 3 A schematic diagram of the output pulse train corresponding to the typical output parameter 1 provided in Example 1.

[0026] Figure 4 A schematic diagram of the output pulse width corresponding to the typical output parameter 2 provided in Example 1.

[0027] Figure 5 A schematic diagram of the output pulse train corresponding to the typical output parameter 2 provided in Example 1.

[0028] Figure 6 A schematic diagram of the output pulse width corresponding to the typical output parameter 3 provided in Example 1.

[0029] Figure 7 A schematic diagram of the output pulse train corresponding to the typical output parameter 3 provided in Example 1.

[0030] The components are as follows: 1. Seed source; 2. Acousto-optic external modulation module; 3. First optical isolator; 4. First acousto-optic modulator; 5. First driver; 6. Generator; 7. Fiber amplifier; 8. First pump source; 9. Wavelength division multiplexer; 10. Single-mode ytterbium-doped gain fiber; 11. Second optical isolator; 12. First bandpass filter; 13. Second pump source; 14. Bundle combiner; 15. Double-clad ytterbium-doped gain fiber; 16. Cladding optical mode stripper; 17. Second bandpass filter; 18. Third optical isolator; 19. Acousto-optic pulse pickup module; 20. Coupler; 21. Second acousto-optic modulator; 22. Second driver; 23. Collimator. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0032] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0033] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form as well. Furthermore, it should be understood that the terms “comprising” and “including”, and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such process, method, product, or apparatus.

[0034] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0035] This invention addresses four major technical challenges: limited internal modulation performance, rigid parameter adjustment, noise interference, and complex structure. Through external modulation technology, coordinated control of dual acousto-optic modulators, noise suppression design, and fiber optic integration, it achieves 1030nm single-frequency pulsed laser output with high stability (narrow linewidth), high flexibility (adjustable parameters), and high signal-to-noise ratio, breaking through existing technological bottlenecks. External modulation involves modulating the generated laser light after it has been produced using an external modulator. The modulator utilizes certain physical effects (such as electro-optic and acousto-optic effects) to alter the characteristics of the laser without directly affecting the laser generation process. This method occurs after laser generation and therefore has no impact on the laser's wavelength stability or linewidth.

[0036] This invention utilizes dual acousto-optic modulators for external modulation. The dual modulators are used to control the laser pulse width and repetition rate, respectively, thereby achieving a single-frequency laser output with a repetition rate of 1030nm and a customizable pulse width. The main technical solution includes: a seed source 1 outputting laser light; an acousto-optic external modulation module 2, which outputs a pulse signal with a set pulse width and modulates the laser light according to the set pulse width to obtain a pulsed laser signal; two-stage fiber amplifiers, which sequentially amplify the pulsed laser signal; an acousto-optic pulse pickup module 19, which modulates the amplified signal according to the set pulse width pulse signal at different set frequency division ratios to obtain single-frequency pulsed laser signals with different repetition frequencies; and a collimator 23 outputting the single-frequency pulsed laser signal. By using dual acousto-optic modulators for external modulation, controlling the laser pulse width and repetition rate respectively, a single-frequency laser output with a repetition rate of 1030nm and a customizable pulse width can be achieved.

[0037] This invention surpasses existing technologies in terms of parameter flexibility, noise suppression, system stability, and cost-effectiveness, providing a customized, high signal-to-noise ratio, narrow linewidth 1030nm single-frequency laser solution for high-precision lidar, lithography, and spectral analysis. Specifically: (1) Independent parameter control: The pulse width (10-30ns) and repetition frequency (500Hz-1kHz) are controlled by dual acousto-optic modulators respectively, breaking through the limitations of traditional internal modulation parameter coupling and realizing highly flexible customized output.

[0038] (2) Ultra-narrow linewidth and high stability: External modulation technology avoids direct intervention in the laser generation process, output linewidth <50kHz (traditional technology >100kHz), and wavelength stability (fluctuation <0.1nm) is significantly improved.

[0039] (3) Noise suppression and high signal-to-noise ratio: Combining two-stage bandpass filtering (bandwidth 2nm) with an acousto-optic pulse pickup module, ASE noise is effectively filtered out, and the signal-to-noise ratio is >50dB (traditional technology <30dB).

[0040] (4) All-fiber integrated design: The system adopts polarization-maintaining fiber fusion splicing and three-level optical isolator, which makes the system compact, strong anti-interference, reduces cost by more than 30%, and has better reliability than traditional electro-optic modulation schemes.

[0041] (5) Power scalability: The two-stage amplification (single-mode and double-clad amplification) design balances noise and power requirements, with an output power of up to 0.56W (typical value), and supports further amplification to the watt level through Yb:YAG crystal.

[0042] Example 1: This example provides a dual acousto-optic modulated single-frequency fiber laser, such as... Figure 1 As shown, it includes: Seed source 1, used for laser output; The acousto-optic external modulation module 2 includes a generator 6 and a first acousto-optic modulator 4. The generator 6 is used to output a pulse signal with a set pulse width, and the first acousto-optic modulator 4 is used to modulate the laser according to the pulse signal with the set pulse width to obtain a pulsed laser signal. The fiber amplifier 7 includes a first-stage single-mode fiber amplifier and a second-stage double-clad fiber amplifier. The two fiber amplifiers are used to amplify the pulsed laser signal in sequence to obtain an amplified signal. The acousto-optic pulse pickup module 19 includes a driver and a second acousto-optic modulator 21. The driver is used to set the frequency division ratio, and the second acousto-optic modulator 21 is used to modulate the amplified signal according to the pulse signal with a set pulse width at different set frequency division ratios to obtain single-frequency pulse laser signals with different repetition frequencies. Collimator 23 is used to output a single-frequency pulse laser signal.

[0043] In this embodiment, the seed source 1 is a linearly polarized 1030nm distributed feedback laser (DFB) single-frequency laser source with a maximum output power of 50mW and a laser linewidth of 10kHz.

[0044] In this embodiment, the acousto-optic external modulation module 2 includes a generator 6, a first driver 5, and a first acousto-optic modulator 4; The generator 6 is an arbitrary waveform generator, which can output a pulse signal with arbitrary pulse width. In this embodiment, the pulse signal has a repetition frequency of 1.5MHz, a pulse width of 10ns, a rise / fall edge of 2ns, and an amplitude of 5V as an example. The pulse signal output by the generator 6 is driven by the first driver 5, which sends a driving signal to drive the first acousto-optic modulator 4 to modulate the laser according to the pulse signal with the set pulse width.

[0045] It is understandable that the modulation process of the laser by the first acousto-optic modulator 4 is existing technology and is not specifically limited. For example, the first acousto-optic modulator 4 is composed of a lithium niobate crystal, an acousto-optic transducer, and a sound-absorbing device.

[0046] As an alternative implementation, the seed source 1 and the first acousto-optic modulator 4 are isolated by a first optical isolator 3.

[0047] In this embodiment, the acousto-optic pulse pickup module 19 includes a coupler 20, a second driver 22, and a second acousto-optic modulator 21. The coupler 20 has a coupling ratio of 1:99, is coated with an anti-reflection film at 1030 nm, and its 1% output port provides a reference signal light to the acousto-optic pulse pickup module 19. The second driver 22 is used to set the frequency division ratio, and the second acousto-optic modulator 21 modulates the amplified signal according to a pulse signal with a set pulse width at different set frequency division ratios to obtain single-frequency pulse laser signals with different repetition frequencies.

[0048] The second driver 22 is also used to set the delay time, and the second acousto-optic modulator 21 modulates the single-frequency pulse laser signal to synchronize it with the reference signal light pulse according to the set delay time and the reference signal light.

[0049] In this embodiment, the pulse division ratio of the acousto-optic pulse pickup module 19 can be adjusted over a wide range. By adjusting the division ratio, the repetition frequency of the single-frequency pulse laser signal can be changed, and by adjusting the delay time, it can be synchronized with the reference signal optical pulse.

[0050] Understandably, the modulation process of the second acousto-optic modulator 21 is existing technology. As long as it can change the repetition frequency of the single-frequency pulse laser signal and adjust the delay time to synchronize it with the reference signal optical pulse, no specific limitations are made here.

[0051] In this embodiment, the single-frequency pulse laser signal output by the acousto-optic pulse pickup module 19 is output through the collimator 23. The collimator 23 has a working distance of 500mm and a loss of less than 0.1dB at 1030nm. The collimator is fixed by a clamp.

[0052] In this embodiment, the fiber amplifier 7 includes two stages, specifically a first-stage single-mode fiber amplifier and a second-stage double-clad fiber amplifier. Specifically: The first-stage single-mode fiber amplifier includes: a first pump source 8, a wavelength division multiplexer 9, a single-mode ytterbium-doped gain fiber 10, a second optical isolator 11, and a first bandpass filter 12.

[0053] The first pump source 8 adopts a forward pumping method, uses a 976nm single-mode continuous pump source, has a maximum output power of 1W, and is output through 105 / 125 optical fiber coupling. The passive fiber device in the first-stage single-mode fiber amplifier uses single-mode polarization-maintaining fiber PM980, single-mode ytterbium-doped fiber. The PM980 gain fiber is 80mm long and its cladding is made of high-purity quartz glass. The fiber core is uniformly doped with a diameter of 5.5 μm, a cladding diameter of 125 μm, and a coating diameter of 250 μm.

[0054] The second-stage double-clad fiber amplifier includes a second pump source 13, a bundler 14, a double-clad ytterbium-doped gain fiber 15, a clad optical mode stripper 16, and a second bandpass filter 17. The second pump source 13 adopts a forward pumping method, uses a 976nm multimode continuous pump source, has a maximum output power of 9W, and is output through 105 / 125 optical fiber coupling. The passive fiber device in the second-stage double-clad fiber amplifier uses a large-mode-field double-clad 10-125 polarization-maintaining fiber, while the active gain fiber is ytterbium-doped. The double-clad 10 / 125 polarization-maintaining fiber 15 is 100 mm long and uses high-purity quartz glass as its cladding. The fiber core is uniformly doped, with a core diameter of 10.5 μm, a cladding diameter of 125 μm, and a coating diameter of approximately 250 μm.

[0055] As an alternative implementation, the cladding mode stripper 16 has a stripping efficiency of more than 99.5% for pump light at 976nm and a reflectivity of less than 0.1% for signal light at 1030nm.

[0056] As an alternative implementation, both the beam combiner 14 and the wavelength division multiplexer 9 have three ports: a signal light port, a pump light port, and an output port. The internal spatial structure devices are all coated with a 1030nm high-transmittance film layer, which has a transmittance of more than 99.5% for signal light.

[0057] As an alternative implementation, the bandwidth of the first bandpass filter 12 and the second bandpass filter 17 are both 2nm, the maximum allowable power is 5W, and only laser light in the range of 1029-1031nm is allowed to pass through.

[0058] As an alternative implementation, the single-mode ytterbium-doped gain fiber 10 and the first bandpass filter 12 are isolated by a second optical isolator 11, and the second bandpass filter 17 and the coupler 20 are isolated by a third optical isolator 18.

[0059] In this embodiment, the working process of the fiber amplifier is as follows: In the first-stage single-mode fiber amplifier, the 1.5MHz, 10ns linearly polarized single-frequency pulsed laser signal generated by the acousto-optic external modulation module 2 enters the single-mode ytterbium-doped gain fiber 10 through the wavelength division multiplexer 9. Under the pumping action of the first pump source 8, the 1030nm pulsed laser signal is amplified and then filtered out by the first bandpass filter 12 to remove the remaining pump light and spontaneous emission (ASE) components, thereby improving the signal-to-noise ratio of the 1030nm pulsed laser signal and obtaining a first-stage amplified 1030nm pulsed laser signal.

[0060] In the second-stage double-clad fiber amplifier, the 1030nm pulsed laser signal is amplified to 121mW by the first-stage single-mode fiber amplifier. The first-stage amplified 1030nm pulsed laser signal enters the second-stage double-clad fiber amplifier through the second optical isolator 11. Then, it and the pump light emitted from the second pump source 13 enter the double-clad ytterbium-doped gain fiber 15 through different ports of the combiner 14. During this process, the first-stage amplified 1030nm pulsed laser signal is amplified again. Then, together with the remaining pump light, it passes through the cladding optical mode stripper 16. The remaining 976nm pump light is stripped in the cladding optical mode stripper 16 and then filtered out by the second bandpass filter 17 to remove the spontaneous emission ASE component, resulting in the second-stage amplified 1030nm pulsed laser signal. This signal continues to pass through the third optical isolator 18 to prevent the return light from damaging the preceding fiber devices.

[0061] The power of the 1030nm pulsed laser signal is amplified to 0.56W through a two-stage fiber amplifier. The 0.56W signal light after two-stage amplification contains some spontaneous emission (ASE) components. The repetition frequency is managed and continuous components are filtered out by the acousto-optic pulse pickup module 19. Specifically, by adjusting the division ratio and delay time parameters of the second driver 22 on the host computer, when the division ratio is set to 1500 and 3000 respectively, single-frequency pulsed laser signals with repetition frequencies of 1kHz and 500Hz can be obtained, respectively. The pulse width is maintained at 10ns, the laser linewidth is less than 50kHz, the maximum output power is 2mW, and the signal-to-noise ratio is greater than 50dB.

[0062] Specifically, when the pulse width of generator 6 in the acousto-optic external modulation module 2 is set to 20ns, single-frequency pulse laser signals with repetition frequencies of 1kHz and 500Hz can be obtained through subsequent processes, with a corresponding pulse width of 20ns.

[0063] Therefore, the final output laser pulse width can be changed by adjusting the parameters of the acousto-optic external modulation module 2, and the repetition frequency of the final output laser can be changed by adjusting the parameters of the acousto-optic pulse pickup module 19, so as to achieve the output of a 1030nm single-frequency pulse laser with customizable repetition frequency and pulse width.

[0064] The following are typical output parameters: Parameter 1: Repetition rate 1kHz, pulse width 10.40ns, maximum output power 2mW, power fluctuation RMS less than 0.8%, laser linewidth less than 50kHz, signal-to-noise ratio greater than 50dB. Output pulse width and pulse train are as follows: Figure 2-3 As shown, a laser output with a pulse width of 10.40 ns was achieved, corresponding to a repetition frequency (PER) of 1000 Hz.

[0065] Parameter 2: Repetition frequency 1kHz, pulse width 20.33ns, maximum output power 5.1mW, power fluctuation RMS less than 1%, laser linewidth less than 50kHz, signal-to-noise ratio greater than 50dB. Output pulse width and pulse train are as follows: Figure 4-5 As shown, a laser output with a pulse width of 20.33 ns was achieved, corresponding to a repetition frequency (PER) of 1000 Hz. Compared with parameter 1, the pulse width can be freely adjusted under the condition of the same repetition frequency.

[0066] Parameter 3: Repetition rate 500Hz, pulse width 10.25ns, maximum output power 1.08mW, power fluctuation RMS less than 0.8%, laser linewidth less than 50kHz, signal-to-noise ratio greater than 50dB. Output pulse width and pulse train are as follows... Figure 6-7 As shown, a laser output with a pulse width of 10.25 ns was achieved, corresponding to a repetition frequency (PER) of 500 Hz. Compared with parameter 1, the repetition frequency can be freely adjusted under the same pulse width.

[0067] Depend on Figure 3 , Figure 5 and Figure 7 As can be seen, the output pulse train is evenly and orderly distributed, and the amplitude of each pulse is stable at about 1 V, showing good periodicity and amplitude stability.

[0068] In summary, according to the above Figure 2-7 The output results show that the above-mentioned dual acousto-optic modulated single-frequency fiber laser achieves stable output of 1030nm pulsed single-frequency fiber laser with continuously adjustable repetition frequency and pulse width within a certain range, high signal-to-noise ratio, and linewidth less than 50kHz.

[0069] Example 2: This example proposes a method for operating a dual acousto-optic modulated single-frequency fiber laser, including: Laser is output from seed source 1; In the acousto-optic external modulation module 2, the generator 6 outputs a pulse signal with a set pulse width, and the first acousto-optic modulator 4 modulates the laser according to the pulse signal with the set pulse width to obtain a pulsed laser signal. The pulsed laser signal is amplified sequentially by a first-stage single-mode fiber amplifier and a second-stage double-clad fiber amplifier to obtain the amplified signal. In the acousto-optic pulse pickup module 19, the repetition frequency of the amplified signal is managed. The frequency division ratio is set by the second driver 22, and the second acousto-optic modulator 21 modulates the amplified signal according to the pulse signal with the set pulse width at different frequency division ratios to obtain single-frequency pulse laser signals with different repetition frequencies. The pulse width is determined by the generator 6 in the acousto-optic external modulation module 2. Finally, the collimator 23 outputs a single-frequency pulse laser signal, and the high extinction ratio of the acousto-optic modulator in the acousto-optic pulse pickup module 19 is used to successfully filter out the spontaneous emission component in the fiber amplifier, thereby improving the extinction ratio of the signal light.

[0070] Example 3: Unlike Example 1, when the pulse width of generator 6 in the acousto-optic external modulation module 2 is set to 30ns, single-frequency pulsed laser signals with repetition frequencies of 1kHz and 500Hz can be obtained through subsequent processes, with a corresponding pulse width of 30ns. This further confirms that the final output laser pulse width can be changed by adjusting the parameters of the acousto-optic external modulation module 2, and the repetition frequency of the final output laser can be changed by adjusting the parameters of the acousto-optic pulse pickup module 19, thus achieving the output of a 1030nm single-frequency pulsed laser with customizable repetition frequency and pulse width.

[0071] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A dual acousto-optic modulated single-frequency fiber laser, characterized in that, include: Seed source, used for laser output; An acousto-optic external modulation module includes a generator and a first acousto-optic modulator. The generator is used to output a pulse signal with a set pulse width, and the first acousto-optic modulator is used to externally modulate the laser according to the pulse signal with the set pulse width to obtain a pulsed laser signal. The fiber amplifier includes a first-stage single-mode fiber amplifier and a second-stage double-clad fiber amplifier, which are used to sequentially amplify the pulsed laser signal to obtain an amplified signal. An acousto-optic pulse pickup module includes a driver and a second acousto-optic modulator. The driver is used to set a frequency division ratio, and the second acousto-optic modulator is used to modulate the amplified signal according to the pulse signal with the set pulse width at different set frequency division ratios to obtain single-frequency pulse laser signals with different repetition frequencies. A collimator is used to output the single-frequency pulse laser signal.

2. The dual acousto-optic modulated single-frequency fiber laser according to claim 1, characterized in that, The first-stage single-mode fiber amplifier includes a single-mode continuous pump source, a wavelength division multiplexer, a single-mode ytterbium-doped gain fiber, and a first bandpass filter. The pulsed laser signal enters the single-mode ytterbium-doped gain fiber through the wavelength division multiplexer, is amplified under the pumping action of the single-mode continuous pump source, and then passes through the first bandpass filter to filter out the remaining pump light and spontaneous emission (ASE) components, thus obtaining a first-stage amplified pulsed laser signal.

3. The dual acousto-optic modulated single-frequency fiber laser according to claim 2, characterized in that, The single-mode continuous pump source adopts a forward pumping method and is a 976nm single-mode continuous pump source.

4. The dual acousto-optic modulated single-frequency fiber laser according to claim 2, characterized in that, The length of the single-mode ytterbium-doped gain fiber is 80 mm.

5. The dual acousto-optic modulated single-frequency fiber laser according to claim 1, characterized in that, The second-stage double-clad fiber amplifier includes a multimode continuous pump source, a combiner, a double-clad ytterbium-doped gain fiber, a cladding mode stripper, and a second bandpass filter. The first-stage amplified pulsed laser signal obtained by the first-stage single-mode fiber amplifier and the pump light emitted by the multimode continuous pump source enter the double-clad ytterbium-doped gain fiber through different ports of the combiner and are amplified again. Then, together with the remaining pump light, they pass through the cladding mode stripper, where the remaining pump light is stripped. The spontaneous emission (ASE) component is then filtered out by the second bandpass filter to obtain the second-stage amplified pulsed laser signal.

6. The dual acousto-optic modulated single-frequency fiber laser according to claim 5, characterized in that, The multimode continuous pump source adopts a forward pumping method and is a 976nm multimode continuous pump source; the length of the double-clad ytterbium-doped gain fiber is 100mm.

7. The dual acousto-optic modulated single-frequency fiber laser according to claim 1, characterized in that, The seed source is isolated from the first acousto-optic modulator by a first optical isolator; the single-mode ytterbium-doped gain fiber is isolated from the first bandpass filter by a second optical isolator; and the second bandpass filter is isolated from the acousto-optic pulse pickup module by a third optical isolator.

8. The dual acousto-optic modulated single-frequency fiber laser according to claim 1, characterized in that, The acousto-optic pulse pickup module also includes a coupler for outputting a reference signal light; the driver is also used to set a delay time, and the second acousto-optic modulator modulates the single-frequency pulse laser signal to synchronize it with the reference signal light pulse according to the set delay time and the reference signal light.

9. The dual acousto-optic modulated single-frequency fiber laser according to any one of claims 1 to 8, characterized in that, The output single-frequency pulsed laser has a center wavelength of 1030nm, a repetition frequency adjustable from 500Hz to 1kHz, a pulse width adjustable from 10ns to 30ns, an output linewidth of less than 50kHz, a signal-to-noise ratio greater than 50dB, and a long-term power fluctuation of less than 1%.

10. A method for operating a dual acousto-optic modulated single-frequency fiber laser as described in any one of claims 1 to 9, characterized in that, Includes the following steps: Laser output from seed source; A pulse signal with a set pulse width is output by the generator, and the first acousto-optic modulator externally modulates the laser according to the pulse signal with the set pulse width to obtain a pulsed laser signal; The pulsed laser signal is amplified sequentially by a first-stage single-mode fiber amplifier and a second-stage double-clad fiber amplifier to obtain an amplified signal. The frequency division ratio is set by the driver, and the amplified signal is modulated by the second acousto-optic modulator according to the pulse signal with the set pulse width at different frequency division ratios to obtain single-frequency pulse laser signals with different repetition frequencies. The collimator outputs the single-frequency pulse laser signal.

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