All-fiber stimulated Brillouin scattering pulse generation method and device

Abstract

The invention provides an all-fiber stimulated Brillouin scattering pulse generation method and device, and the method comprises the steps: providing stable seed laser through a seed source, endowing the seed laser with a periodic regulation and control characteristic through a modulation structure, amplifying the modulated seed laser through a laser amplification system, and enabling the amplified seed laser to serve as Brillouin pump light, and the SBS effect is periodically triggered by utilizing the Brillouin pump light in the gain optical fiber, and finally the Stokes pulse light which is periodically and reversely propagated is generated and output. The SBS pulse laser has the advantages of being compact in structure, high in environmental adaptability and easy to integrate, the pulse repetition frequency can be precisely controlled, the pulse output characteristics of narrow linewidth and narrow pulse width can be achieved, and a practical SBS pulse laser solution can be provided for the field with high requirements for time sequence precision and system stability.

Description

Technical Field

[0001] This application relates to the field of fiber laser technology, and in particular to a method and apparatus for generating stimulated Brillouin scattering pulses in an all-fiber environment. Background Technology

[0002] Stimulated Brillouin scattering (SBS) is a key third-order nonlinear optical effect in laser technology. Its physical essence lies in the interaction between incident light waves and acoustic waves in a medium, producing scattered light with significant backpropagation characteristics. Due to its core characteristics of low threshold power, narrow gain bandwidth, and high back reflectivity, the SBS effect provides crucial technical support for the development of pulsed laser technology, demonstrating significant application potential in pulsed laser generation, laser beam quality optimization, and laser pulse width compression.

[0003] Currently, pulsed laser technologies based on the SBS effect mainly include SBS Q-switched lasers, SBS phase conjugation techniques, and SBS pulse compression techniques. However, existing SBS-based pulsed laser technologies still have significant limitations in practical applications: on the one hand, SBS Q-switched lasers suffer from unstable repetition rates and difficulty in precisely controlling pulse timing; on the other hand, SBS phase conjugation and pulse compression techniques typically rely on solid-state or hybrid system architectures, which have poor structural compactness and stability, and are difficult to integrate.

[0004] As laser technology develops towards miniaturization, integration, and high stability, there is an urgent need to develop an SBS pulse generation method and device that combines the advantages of an all-fiber structure with precise timing control capabilities, in order to break through existing technological bottlenecks and promote the practical application of SBS pulsed laser technology. Summary of the Invention

[0005] This application aims to at least partially address one of the technical problems in the related art.

[0006] Therefore, the first objective of this application is to propose an all-fiber stimulated Brillouin scattering pulse generation device and method.

[0007] To achieve the above objectives, a first aspect of this application provides an all-fiber stimulated Brillouin scattering pulse generation device, comprising: A laser pumping module includes a seed source, a modulation structure, and a laser amplification system. The seed source is used to generate a seed laser, the modulation structure is used to modulate the seed laser, and the laser amplification system is used to amplify the modulated seed laser and use it as a Brillouin pump light. The Brillouin pump light has a periodic intensity distribution in the time domain or has a periodic SBS threshold modulation capability. A pulse generation module, connected to the laser pump module, includes a gain fiber; the pulse generation module is used to further amplify the Brillouin pump light and periodically trigger stimulated Brillouin scattering within the gain fiber to generate and output periodically backpropagating Stokes pulses.

[0008] Optionally, the pulse generation module further includes a first isolator, a coupler, and a beam combiner connected in sequence, and a pump source connected to the beam combiner. The first isolator is disposed in the optical path between the coupler and the laser pump module to block the input of the back-propagating optical signal to the laser pump module. The beam combiner is disposed in the optical path between the gain fiber and the coupler and is connected to the pump source to combine the Brillouin pump light and the continuous pump light output by the pump source and output them to the gain fiber, and to output the back-propagating Stokes pulse to the coupler.

[0009] Optionally, it further includes a pulse monitoring and feedback control module, the input of which is connected to the pulse output of the coupler, for monitoring the pulse parameters of the Stokes pulse light output by the coupler; the output of which is connected to the laser pump module and the pump source, for feeding back the modulation parameters and laser parameters of the Brillouin pump light based on the monitoring results; wherein, The pulse parameters of the Stokes pulse light include pulse shape, pulse repetition frequency, pulse width, and power parameters; the modulation parameters of the Brillouin pump light include modulation frequency, modulation period, duty cycle, modulation depth, and modulation bandwidth; the laser parameters of the Brillouin pump light include the seed source and the output power of the pump source.

[0010] Optionally, the modulation structure includes a current control system connected to the seed source, which outputs a rectangular modulation current signal to the seed source to generate the seed laser with rectangular intensity modulation. Alternatively, the modulation structure includes an electro-optic modulator, a radio frequency amplifier connected to the electro-optic modulator, and a signal generator connected to the radio frequency amplifier; wherein, The signal generator is used to generate and output modulated electrical signals; The radio frequency amplifier is used to receive the modulated electrical signal and amplify the modulated electrical signal before outputting it. The electro-optic modulator is connected to the seed source and the electro-optic modulator respectively, and is used to receive the seed laser output by the seed source and the modulated electrical signal after power amplification, and to perform intensity modulation or phase modulation on the seed laser based on the modulated electrical signal after power amplification.

[0011] Optionally, the electro-optic modulator includes one of an intensity modulator or a phase modulator; wherein, When the electro-optic modulator is the intensity modulator, the modulated electrical signal generated by the signal generator is a rectangular modulated electrical signal; In the case of the phase modulator, the modulated electrical signal generated by the signal generator is a continuously variable frequency electrical signal or a switching electrical signal that periodically switches between a constant electrical signal and a sinusoidal electrical signal, a white noise electrical signal, or a PRBS electrical signal.

[0012] Optionally, when the input Brillouin pump light is subjected to rectangular or intensity modulation, the pulse generation module will form periodically distributed illuminated and dark regions in the time domain within the gain fiber; wherein, The Brillouin pump light triggers stimulated Brillouin scattering in the illuminated region and generates periodically back-propagating Stokes pulses; the Brillouin pump light does not trigger stimulated Brillouin scattering in the dark region and does not generate periodically back-propagating Stokes pulses, and the light intensity of the Brillouin pump light in the illuminated region is greater than the light intensity in the dark region. Alternatively, when the pulse generation module receives a phase-modulated Brillouin pump, it will form a first region and a second region that are periodically distributed in the time domain within the gain fiber; wherein... The Brillouin pump light triggers stimulated Brillouin scattering in the first region and generates periodically back-propagating Stokes pulses; the Brillouin pump light does not trigger stimulated Brillouin scattering in the second region and does not generate periodically back-propagating Stokes pulses, and the SBS threshold corresponding to the first region is lower than the SBS threshold corresponding to the second region.

[0013] To achieve the above objectives, a second aspect of this application provides a method for generating stimulated Brillouin scattering pulses in an all-fiber optic manner, comprising: A seed laser and a modulation signal are provided. The seed laser is modulated using the modulation signal and amplified to serve as a Brillouin pump light. The Brillouin pump light has a periodic intensity distribution in the time domain or has a periodic SBS threshold modulation capability. The Brillouin pump light is further amplified and periodically triggered by the Brillouin pump light to generate and output periodically backpropagating Stokes pulses.

[0014] Optionally, the step of modulating the seed laser using the modulation signal and amplifying it to serve as the Brillouin pump light includes: A rectangular modulated current signal is output to the seed source using a current control system. The seed source is made to generate a seed laser with rectangular intensity modulation by using a rectangular modulation current signal; The seed laser is output to a laser amplification system by rectangular modulation of light intensity, thereby forming the Brillouin pump light with a periodic intensity distribution in the time domain.

[0015] Optionally, the step of modulating the seed laser using the modulation signal and amplifying it to serve as the Brillouin pump light includes: A rectangular modulated electrical signal is generated and output using a signal generator; The rectangular modulated electrical signal is amplified using a radio frequency amplifier; The intensity modulator receives the seed laser and the power-amplified rectangular modulation electrical signal, and performs rectangular modulation on the light intensity of the seed laser based on the power-amplified rectangular modulation electrical signal; The seed laser, after undergoing rectangular intensity modulation, is output to a laser amplification system for amplification, forming the Brillouin pump light with a periodic intensity distribution in the time domain.

[0016] Optionally, the step of modulating the seed laser using the modulation signal and amplifying it to serve as the Brillouin pump light includes: A signal generator is used to generate and output continuously variable frequency electrical signals or periodically switching electrical signals; The power of the continuously variable frequency electrical signal or the periodically switched electrical signal is amplified using a radio frequency amplifier; The phase of the seed laser is modulated based on the power-amplified continuous frequency conversion electrical signal or the periodically switched switching electrical signal, using a phase modulator to receive the seed laser and the power-amplified continuous frequency conversion electrical signal or the periodically switched switching electrical signal. The phase-modulated seed laser is output to a laser amplification system for amplification, forming the Brillouin pump light that can generate a periodic SBS threshold distribution in the gain fiber in the time domain.

[0017] The all-fiber SBS pulse generation method and apparatus provided in this application have at least the following beneficial effects: This application provides an all-fiber SBS pulse generation method and apparatus, including providing a stable seed laser using a seed source, imparting periodic modulation characteristics to the seed laser using a modulation structure, amplifying the modulated seed laser into Brillouin pump light using a laser amplification system, and periodically triggering the SBS effect using the Brillouin pump light in the gain fiber, ultimately generating and outputting periodically back-propagating Stokes pulses. This application offers advantages such as compact structure, strong environmental adaptability, and ease of integration, and can achieve precise controllable pulse repetition frequency, as well as narrow linewidth and narrow pulse width pulse output characteristics. It provides a practical SBS pulsed laser solution for fields with high requirements for timing accuracy and system stability.

[0018] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0019] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a schematic diagram of an all-fiber SBS pulse generation device according to an embodiment of this application.

[0020] Figure 2 This is a schematic diagram of a laser pumping module according to an embodiment of this application.

[0021] Figure 3 This is a schematic diagram of another laser pumping module according to an embodiment of this application.

[0022] Figure 4 This is a schematic diagram of the intensity distribution of a Brillouin pump light according to an embodiment of this application.

[0023] Figure 5 This is a schematic diagram illustrating the threshold distribution of a Brillouin pump light-triggered stimulated Brillouin scattering effect according to an embodiment of this application.

[0024] Figure 6 This is a schematic diagram of an SBS pulse output waveform under phase modulation according to an embodiment of this application.

[0025] Figure 7 for Figure 6 A magnified view of the waveform of a pulse sequence.

[0026] Figure 8 This is a schematic diagram of another phase-modulated SBS pulse output waveform according to an embodiment of this application.

[0027] Figure 9 for Figure 8 A magnified view of a pulse sequence waveform. Detailed Implementation

[0028] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0029] Currently, pulsed laser technologies based on the SBS effect mainly include SBS Q-switched lasers, SBS phase conjugation technology, and SBS pulse compression technology. Among them, SBS Q-switched lasers, relying on the synergistic effect of random distributed feedback and the SBS effect, can directly output pulsed lasers with narrow linewidths and narrow pulse widths. However, the repetition frequency of its output pulses is unstable, and the pulse timing is difficult to control precisely, limiting its application in fields requiring high timing accuracy, such as lidar and spectral detection. SBS phase conjugation technology and SBS pulse compression technology are mainly applied to solid-state lasers or hybrid laser systems. The former effectively improves beam quality by using the backscattered Stokes light generated by the SBS effect to compensate for the wavefront distortion of the laser system; the latter, based on the energy transfer characteristics of the Brillouin amplification process, can compress wide pulses on the nanosecond scale to narrow pulses on the sub-nanosecond scale. Both achieve their function by injecting pulsed light into the SBS medium to trigger backscattering. Although the physical mechanisms of these two technologies provide inspiration for the timing control of SBS pulses, their system architectures typically rely on non-all-fiber structures that include free-space optical paths, making it difficult to meet the technical requirements of laser devices for compact structure, high stability, and easy integration.

[0030] Based on the above problems, this application provides an all-fiber SBS pulse generation method and apparatus, which can specifically solve the problems of unstable repetition frequency and difficulty in precise control of pulse timing in existing SBS Q-switched lasers, as well as the problems of non-compact structure, insufficient stability and difficulty in integration caused by the reliance on non-all-fiber architecture for SBS phase conjugation and pulse compression technology. This involves modulating the seed laser generated by the seed source using a modulation structure in the laser pump module, and then amplifying it through a laser amplification system to form a Brillouin pump light with a periodic intensity distribution in the time domain or with periodic SBS threshold control capability. This active modulation method precisely controls the triggering timing of the SBS process, solving the problems of unstable repetition frequency and difficult timing control. The pulse generation module further amplifies the Brillouin pump light and periodically triggers the stimulated Brillouin scattering process in the gain fiber, generating and outputting periodically back-propagating Stokes pulses to ensure the regularity of pulse output. At the same time, by using an all-fiber architecture laser pump module and pulse generation module in synergy, the traditional non-all-fiber system is replaced, achieving both stable pulse repetition frequency and precise timing control, while also meeting the technical requirements of compact structure, high stability, and easy integration of laser equipment.

[0031] According to the first aspect of this application, an all-fiber SBS pulse generation device is provided, such as... Figures 1-3 As shown, the device includes a laser pumping module and a pulse generation module. The laser pumping module includes a seed source, a modulation structure, and a laser amplification system; the pulse generation module is connected to the laser pumping module and includes a gain fiber.

[0032] Understandably, seed sources are used to generate seed lasers as the basic light source, providing a stable optical signal foundation for subsequent modulation and amplification stages. These include single-frequency lasers or narrow-linewidth lasers, such as fiber-coupled semiconductor lasers and fiber lasers. The lasers they output have the characteristics of narrow linewidth and stable wavelength, laying the foundation for subsequent laser modulation to generate Brillouin pump light and trigger the SBS effect to generate narrow-linewidth Stokes pulses.

[0033] The modulation structure is used to actively modulate the intensity or phase of the seed laser to impart the timing characteristics of periodically triggering the SBS effect. In other words, the modulation structure can enable the Brillouin pump light to have a periodic intensity distribution in the time domain, or to have periodic SBS threshold modulation capability, providing core support for subsequent precise control of the SBS pulse triggering timing.

[0034] The laser amplification system is used to amplify the power of the modulated seed laser to a suitable power level as Brillouin pump light and inject it into the pulse generation module.

[0035] The pulse generation module further amplifies the Brillouin pump light, ensuring its local power reaches the triggering requirements for stimulated Brillouin scattering (SBS) in the gain fiber. This prevents unstable SBS effect generation due to insufficient power and, through amplification of the backward Stokes light, enables higher-power SBS pulse output. Furthermore, the gain fiber, acting as the SBS effect generation medium, triggers the stimulated Brillouin scattering process. Its function is to trigger the interaction between the light wave and phonons when the local power of the Brillouin pump light exceeds the corresponding SBS threshold, generating periodically backpropagating Stokes pulses.

[0036] In summary, this application utilizes a seed source to provide a stable seed laser, employs a modulation structure to impart periodic modulation characteristics to the seed laser, uses a laser amplification system to amplify the modulated seed laser as a Brillouin pump light, utilizes a pulse generation module to further amplify the Brillouin pump light and the amplified backward Stokes light, and utilizes the Brillouin pump light to periodically trigger the SBS effect in the gain fiber, ultimately generating and outputting periodically backpropagating Stokes pulses. The device provided by this application has the advantages of compact structure, strong environmental adaptability, and easy integration, and can achieve precise controllable pulse repetition frequency, narrow linewidth, and narrow pulse width characteristics. It can provide a practical SBS pulsed laser solution for fields with high requirements for timing accuracy and system stability.

[0037] In some embodiments, the pulse generation module further includes a first isolator, a pump source, a coupler, and a beam combiner connected in sequence. The first isolator is disposed in the optical path between the coupler and the laser pump module to block the input of back-propagating optical signals to the laser pump module. The beam combiner is disposed in the optical path between the gain fiber and the coupler, and the pump source is connected to the other output end of the beam combiner, enabling the beam combiner, pump source, and gain fiber to jointly amplify the Brillouin pump light and drive the SBS process; and to achieve higher power SBS pulse output by amplifying the backward Stokes light.

[0038] Understandably, the first isolator is used to block back-propagating optical signals, such as SBS pulses (Stokes pulses) generated in the gain fiber and fiber scattering light, allowing only the Brillouin pump light output from the laser pump module to propagate forward. Its core principle is to utilize optical properties such as the Faraday rotation effect to achieve unidirectional conduction, preventing backlight from interfering with the seed source, modulation structure, and laser amplification system within the laser pump module. This interference could damage the laser amplification system and electro-optic modulator, or disrupt the frequency stability of the seed source. By placing the first isolator in the optical path between the coupler and the laser pump module, backlight can be intercepted midway through its propagation from the coupler to the laser pump module, preventing it from entering the core components of the pump module. This solves problems such as Brillouin pump light power fluctuations, unstable modulation timing, and wavelength shifts caused by backlight interference, ensuring the stability of the laser pump module's output.

[0039] A coupler is used to achieve directional separation and transmission of light according to the propagation direction of the input optical signal. Its core principle is to use an optical fiber coupling structure to split the light equally, allowing the forward-propagating Brillouin pump light to pass smoothly and be transmitted to the combiner, while guiding the backward-propagating SBS pulse light (returning from the gain fiber through the combiner) to its preset pulse output end and outputting it. By placing the coupler in the optical path between the first isolator and the combiner, it can ensure that the forward Brillouin pump light is transmitted from the first isolator to the combiner, preparing for subsequent injection into the gain fiber, and can also guide and output the backward SBS pulse returning from the combiner.

[0040] A beam combiner is used to couple two independent optical signals (Brillouin pump light from the coupler and continuous pump light from the pump source) to the same gain fiber. Its core principle is to use techniques such as fiber fusion taper or waveguide coupling to converge optical signals of different wavelengths or paths within the beam combiner and output them along the same optical path. By placing the beam combiner in the optical path between the gain fiber and the coupler, the Brillouin pump light and the continuous pump light (responsible for providing energy to the gain fiber, further enhancing the Brillouin pump light power, maintaining the power level required for the SBS effect, and simultaneously amplifying the backward SBS pulse) can be synchronously injected into the gain fiber. This solves the problem of insufficient power causing SBS to fail to trigger or unstable pulse generation, ensuring that the local power of the Brillouin pump light can stably exceed the SBS threshold, guaranteeing the continuous generation of periodic Stokes pulses.

[0041] It should be noted that the gain fiber is an active fiber doped with rare-earth elements, such as ytterbium-doped fiber, erbium-doped fiber, or thulium-doped fiber. Active fibers require the aforementioned combiner and pump source to provide energy, thereby enhancing the Brillouin pump light power, maintaining the SBS effect, and amplifying the backward SBS pulse. Alternatively, the gain fiber can be replaced with a passive fiber, such as a highly nonlinear fiber or a non-rare-earth-doped passive fiber. Passive fibers do not require a combiner or external pump source; changing the length of the passive fiber can alter the SBS threshold and support the SBS effect. Therefore, this application does not specifically limit the type of fiber, and when the fiber is passive, there is no need to additionally configure a combiner and pump source to provide continuous pump light.

[0042] Furthermore, the isolation of the first isolator is no less than 20dB, and the coupler is a 1×2 or 2×2 fiber optic coupler, with the splitting ratio selectable as needed. Alternatively, a fiber optic circulator can be used to replace the coupler, as it can also function as an isolator, thus eliminating the need for the first isolator. The beam combiner can be a pumped beam combiner or a laser beam combiner.

[0043] In some embodiments, the device further includes a pulse monitoring and feedback control module, wherein the input terminal of the pulse monitoring and feedback module is connected to the pulse output terminal of the coupler, and the output terminal is connected to the laser pumping module and the pump source.

[0044] Understandably, the pulse monitoring and feedback control module is responsible for monitoring the pulse parameters of the Stokes pulse light output by the coupler in real time, and dynamically adjusting the modulation and laser parameters of the Brillouin pump light, as well as the laser parameters of the pump source, based on the monitoring results, in order to ensure the stability of the pulse parameters of the output SBS pulse.

[0045] By connecting the input terminal of the pulse monitoring and feedback module to the pulse output terminal of the coupler, the pulse monitoring and feedback module can directly acquire the backward Stokes pulse light exported by the coupler, ensuring that the monitored object has the pulse parameters required for actual application and providing a reliable basis for precise adjustment. For example, the pulse output terminal of the coupler can be connected to a 1×2 coupler, allowing the 1×2 coupler to output a portion of the SBS pulse to the pulse monitoring and feedback module for real-time monitoring of pulse parameters.

[0046] Correspondingly, by connecting the output of the pulse monitoring and feedback module to the laser pump module and the pump source, targeted adjustment of the laser pump module can be achieved to adjust the modulation parameters of its internal modulation structure and correct the temporal characteristics of the Brillouin pump light; and feedback adjustment of the output power of the pump source can be achieved to optimize the energy level provided to the gain fiber. Finally, through coordinated adjustment, the repetition frequency, pulse width and other parameters of the SBS pulse can be stabilized within the preset range.

[0047] It should be noted that the pulse parameters of the SBS pulse include, but are not limited to, at least one of the following parameters: pulse shape, pulse repetition frequency, pulse width, and power. The modulation parameters of the modulation structure include, but are not limited to, at least one of the following parameters: modulation frequency, modulation period, duty cycle, modulation depth, and modulation bandwidth. The laser parameters of the Brillouin pump light include the output power of the seed source and the pump source.

[0048] Furthermore, the repetition frequency of the backward SBS pulse is determined by the modulation period, which ranges from ms to hundreds of ns in length, corresponding to a repetition frequency in the kHz to MHz range for the SBS pulse. The pulse width of the SBS pulse is primarily determined by the phonon lifetime of the optical fiber, while the linewidth is mainly determined by the spectral width of the Brillouin pump and the SBS gain spectrum.

[0049] In some embodiments, such as Figure 2 As shown, the modulation structure is a direct modulation structure, including a current control system. The current control system is connected to the seed source and is used to output a rectangular modulation current signal to the seed source to directly modulate the seed laser generated by the seed source.

[0050] It can be understood that the function of the current control system is to achieve direct time-domain modulation of the seed laser intensity by dynamically adjusting the driving current of the seed source. The core is to utilize the correlation between the output intensity of the seed source and the driving current. That is, when the driving current is higher than the lasing threshold of the seed source, the seed source outputs laser, and when the driving current is lower than the lasing threshold, the seed source stops outputting laser.

[0051] Therefore, when the current control system outputs a periodic high-level-low-level alternating rectangular modulated current signal, the seed source can be driven to output laser light and form an illuminated region when the current signal is high; and driven to stop outputting laser light and form a dark region when the current signal is low. Through this on-off current control, the seed source directly outputs a pulse sequence with a rectangular intensity distribution, such as... Figure 4 As shown, its repetition frequency, pulse width and the period and duty cycle of the rectangular modulation current signal are strictly synchronized, ultimately providing a modulated laser with a periodic intensity distribution for the subsequent laser amplification system, laying the foundation for the time-domain triggering of the SBS effect.

[0052] In some embodiments, such as Figure 3 As shown, the modulation structure is an external modulation structure, including an electro-optic modulator, an RF amplifier connected to the electro-optic modulator, and a signal generator connected to the RF amplifier.

[0053] Understandably, the role of the signal generator is to generate a modulated electrical signal with a specific waveform, which serves as the command source for controlling the characteristics of the laser. The parameters of its signal, such as period, frequency, and duty cycle, directly determine the timing and mode of subsequent seed laser modulation, providing a basis for accurately controlling the temporal characteristics of the Brillouin pump light.

[0054] The function of an RF amplifier is to amplify the power of the modulated electrical signal output from the signal generator, ensuring it reaches a suitable power level to drive the electro-optic modulator (the power level primarily depends on the half-wave voltage of the modulator). Since the electro-optic modulator requires a sufficiently strong electrical signal to produce the desired modulation effect, an RF amplifier is needed to amplify the input modulated electrical signal, preventing problems such as insufficient modulation depth, insignificant light intensity, or phase changes due to insufficient signal strength. When the electrical signal generated by the signal generator has sufficiently high power, it can also be used directly to drive the electro-optic modulator without requiring amplification by an RF amplifier.

[0055] The role of an electro-optic modulator is to convert the electrical signal input to an RF amplifier into physical modulation of a laser, such as intensity or phase modulation, based on the electro-optic effect. By converting the continuous laser output from a seed source into a seed laser with targeted modulation characteristics (periodic intensity distribution or periodic SBS threshold modulation capability), the electro-optic modulator provides a crucial temporal control basis for subsequent Brillouin pump light formation and triggering of the SBS effect. Exemplarily, an electro-optic modulator may include one of an intensity modulator and a phase modulator.

[0056] When the electro-optic modulator is an intensity modulator, the modulation electrical signal generated by the signal generator is a rectangular modulation electrical signal. Therefore, the continuous seed laser output from the seed source is split into two beams after entering the intensity modulator. The rectangular modulation electrical signal, amplified by the RF amplifier, changes the phase difference between the two beams and utilizes interference to achieve periodic variations in laser intensity. Ultimately, the continuous seed laser is converted into a rectangular intensity distribution pulse sequence with a high extinction ratio, strictly synchronized with the timing of the rectangular electrical signal. Figure 4 As shown, this provides precise temporal control of light intensity for the subsequent formation of Brillouin pump light that can trigger the SBS effect.

[0057] When the electro-optic modulator is a phase modulator, the modulation signal generated by the signal generator is a continuously variable frequency signal (such as a linear frequency modulated signal), or a switching signal that periodically switches between a constant signal and one of the following: a sinusoidal signal, a white noise signal, or a PRBS signal. Thus, after the continuous seed laser output from the seed source enters the phase modulator, the modulation signal, amplified by the RF amplifier, is loaded onto the phase modulator, periodically changing the SBS threshold state of the laser through phase modulation.

[0058] When the modulating electrical signal is a continuously variable frequency signal, the low-frequency region is characterized by a low SBS threshold and a long SBS accumulation time, while the high-frequency region is characterized by a high SBS threshold and a short SBS accumulation time. Therefore, the SBS threshold of the seed laser will exhibit a periodic distribution of low to high thresholds as the electrical signal frequency changes. When the modulating electrical signal is a switched electrical signal, the SBS threshold periodically switches between the low threshold of a single-frequency laser corresponding to constant electrical signal phase modulation and the high threshold of a spectrally broadened laser corresponding to sinusoidal, white noise, or PRBS phase modulation. This transforms the continuous seed laser into a Brillouin pump light with periodic SBS threshold modulation capability, providing a basis for subsequent precise control of the SBS effect triggering timing.

[0059] For example, such as Figure 5 As shown, the periodic SBS threshold distribution in the time domain can specifically include a periodically distributed first region and a second region. The first region of the Brillouin pump light triggers stimulated Brillouin scattering and generates periodically backpropagating Stokes pulses. Conversely, the second region of the Brillouin pump light does not trigger stimulated Brillouin scattering, does not generate periodically backpropagating Stokes pulses, and the SBS threshold corresponding to the first region is lower than the SBS threshold corresponding to the second region.

[0060] It should be noted that, to prevent backlight from interfering with the seed source and modulation structure within the laser pump module—for example, damaging the electro-optic modulator or disrupting the frequency stability of the seed source—the laser pump module also includes a second isolator. This second isolator is positioned in the optical path between the seed source or electro-optic modulator and the laser amplification system. It intercepts the backlight midway from the laser amplification system to the forward-stage components, preventing it from entering the electro-optic modulator or seed source. This solves problems such as Brillouin pump power fluctuations, modulation timing instability, and wavelength shifts caused by backlight interference, further ensuring the stability of the laser pump module's output.

[0061] In addition, the gain fiber also includes an output end, which is used to duct the residual light that has propagated forward along the gain fiber and has not participated in the SBS effect. The residual light propagating forward refers to unscattered Brillouin pump light and continuous pump light, etc., and in phase modulation mode, it manifests as a dark pulse sequence with the same repetition frequency as the SBS pulse light. The pulse parameters output by the dark pulse sequence depend on the modulation period, duty cycle, and pump source power of the modulating electrical signal.

[0062] According to the second aspect of this application, such as Figure 1 As shown, an all-fiber SBS pulse generation method is provided, which includes using the apparatus described in the first aspect above, and further includes the following steps: S1 provides the seed laser and modulation signal. The seed laser is modulated using the modulation signal and amplified to serve as the Brillouin pump light. The Brillouin pump light has a periodic intensity distribution in the time domain or has a periodic SBS threshold modulation capability. S2, the Brillouin pump light output to the pulse generation module is further amplified, so that the local power of the Brillouin pump light in the gain fiber is greater than the SBS threshold of the corresponding region, periodically triggering the stimulated Brillouin scattering process, and finally generating and outputting periodically backpropagating Stokes pulse light.

[0063] Among them, such as Figure 2 and Figure 4 As shown, step S1, which modulates the seed laser using a modulation signal and amplifies it to serve as the Brillouin pump light, includes: S101 uses a current control system to output a rectangular modulated current signal to the seed source; S102 uses a rectangular modulation current signal to make the seed source generate a seed laser with rectangular modulation of light intensity; S103 outputs the seed laser with rectangular intensity modulation to the laser amplification system for amplification, forming a Brillouin pump light with a periodic intensity distribution in the time domain.

[0064] Alternatively, as an alternative, such as Figure 3 and Figure 4 As shown, step S1, which modulates the seed laser using a modulation signal and amplifies it to serve as the Brillouin pump light, may further include: S111 uses a signal generator to generate and output a rectangular modulated electrical signal; S112 uses an RF amplifier to amplify the power of a rectangular modulated electrical signal; S113 uses an intensity modulator to receive the seed laser and the power-amplified rectangular modulation electrical signal, and performs rectangular modulation on the light intensity of the seed laser based on the power-amplified rectangular modulation electrical signal. S114 outputs the seed laser, after rectangular intensity modulation, to the laser amplification system for amplification, forming a Brillouin pump light with a periodic intensity distribution in the time domain.

[0065] Alternatively, as an alternative, such as Figure 3 and Figure 5 As shown, step S1, which modulates the seed laser using a modulation signal and amplifies it to serve as the Brillouin pump light, may further include: S121 uses a signal generator to generate and output a continuously variable frequency electrical signal or a periodically switching electrical signal; S122 uses an RF amplifier to amplify the power of a continuously variable frequency electrical signal or a periodically switching electrical signal. S123, using a phase modulator to receive the seed laser and the power-amplified continuous frequency conversion electrical signal or the periodically switched switching electrical signal, and modulate the phase of the seed laser based on the power-amplified continuous frequency conversion electrical signal or the periodically switched switching electrical signal. S124 outputs the phase-modulated seed laser to the laser amplification system for amplification, forming a Brillouin pump light that can generate a periodic SBS threshold distribution in the gain fiber in the time domain.

[0066] As an example, in the process of phase modulation based on a continuously variable frequency electrical signal and triggering an SBS pulse, the seed laser is a continuous laser, generated and output by a seed source, and the seed source is a single-frequency DFB laser, whose output power of the continuous laser is 50mW, the center wavelength is 1064nm, and the linewidth is less than 10MHz.

[0067] The continuously variable frequency electrical signal is a linear frequency modulation (LFM) radio frequency signal, generated and output by a signal generator composed of AD9914 chips. The frequency of the LFM radio frequency signal linearly scans from 1MHz to 1000MHz within a set time (one cycle) and satisfies: , , in, The starting frequency is 1MHz. The sweep slope is determined by the bandwidth of the LFM radio frequency signal. and sweep frequency cycle Sure.

[0068] The LFM radio frequency signal after power amplification modulates the phase of the continuous laser output from the seed laser in the phase modulator. The phase modulator is a lithium niobate electro-optic phase modulator with a bandwidth of 10 GHz and a half-wave voltage of Vπ = 5V @ 50 kHz.

[0069] The modulated seed laser passes through a first isolator, a laser amplification system, a second isolator, a coupler, and a beam combiner before being injected into the gain fiber. The gain fiber is a 10-meter-long double-clad ytterbium-doped fiber with a core diameter of 20 μm and a cladding diameter of 400 μm.

[0070] The typical SBS gain bandwidth of a gain fiber is approximately 50 MHz. Based on the influence of modulation frequency on the SBS threshold, frequency bands with modulation frequencies less than two SBS gain bandwidths can be considered low-frequency bands, i.e., frequencies between 1 MHz and 100 MHz. In this band, the gain fiber has a lower SBS threshold and a longer SBS accumulation time, corresponding to the first region of the SBS threshold distribution. Conversely, frequency bands between 100 MHz and 1000 MHz can be considered high-frequency bands. In this band, the gain fiber has a higher SBS threshold and a shorter SBS accumulation time, corresponding to the second region of the SBS threshold distribution. Therefore, when the instantaneous power of the Brillouin pump light exceeds the corresponding SBS threshold and has a sufficiently long SBS accumulation time, a backward-propagating Stokes pulse can be generated.

[0071] In one example, the LFM sweep period is set to 1ms, corresponding to a repetition frequency of 1kHz. For example... Figure 6 and Figure 7 As shown, due to the long duration of the first region, the SBS process has sufficient accumulation time. Thus, the Stokes pulse light is formed as a pulse envelope structure containing multiple sub-pulses, thereby obtaining an SBS pulse envelope output with a repetition frequency of 1 kHz. Each envelope lasts for approximately tens of μs and contains multiple sub-pulses spaced approximately 500 ns apart.

[0072] In another example, the LFM sweep period is shortened to 10 μs, corresponding to a repetition frequency of 100 kHz. For example... Figure 8 and Figure 9 As shown, due to the short duration of the first region, the SBS process can only accumulate to form a single pulse. Therefore, the Stokes pulse light is formed as a single-pulse sequence with a repetition frequency of 100 kHz and a pulse width of approximately 18 ns.

[0073] As an example, in the process of using an electro-optic intensity modulator to modulate the light intensity and trigger the SBS pulse based on the rectangular modulated electrical signal, the seed laser is a continuous laser, generated and output by a seed source, and the seed source is a single-frequency DFB laser, whose output power of the continuous laser is 50mW, the center wavelength is 1064nm, and the linewidth is less than 10MHz.

[0074] The modulation signal is a rectangular modulated electrical signal, which is amplified by an RF amplifier and then applied to an intensity modulator. The intensity modulator is a lithium niobate Mach-Zehnder modulator with a bandwidth of 12 GHz and a half-wave voltage of Vπ = 3.5 V @ 50 kHz. By adjusting the bias voltage and modulation depth of the intensity modulator, rectangular light intensity modulation with an extinction ratio greater than 20 dB is achieved.

[0075] Based on the influence of the rectangular modulated electrical signal on the seed laser, the resulting Brillouin pump light exhibits a periodic intensity distribution in the time domain. Therefore, the Brillouin pump light within the input gain fiber can be divided into illuminated and non-illuminated regions in the time domain. The intensity of the Brillouin pump light in the illuminated region is greater than that in the non-illuminated region. This allows the Brillouin pump light power in the illuminated region to exceed the SBS threshold of the gain fiber, thereby triggering the SBS process and generating a backward Stokes pulse. Conversely, the Brillouin pump light power in the non-illuminated region does not exceed the SBS threshold of the gain fiber, thus not triggering the SBS process and not generating an SBS pulse.

[0076] As an example, in the process of direct light intensity modulation and triggering SBS pulse based on rectangular modulated current signal, the seed laser is composed of a directly modulated semiconductor laser, and the modulation signal is a rectangular modulated current signal provided by a current control system composed of an arbitrary waveform generator and a laser driver.

[0077] The driving current of the seed source is rectangularly modulated by a current control system. The modulation frequency can be adjusted from kHz to MHz, and the duty cycle can be set from 1% to 90%. Thus, when the driving current is higher than the threshold, the seed source outputs laser light, forming an illuminated region within the gain fiber, thereby triggering the SBS process and generating a backward Stokes pulse. When the driving current is lower than the threshold, the seed source does not output light, forming a dark region within the gain fiber, thus not triggering the SBS process and not generating an SBS pulse.

[0078] In summary, this application provides a seed laser and a modulation signal, modulates and amplifies the seed laser to form a Brillouin pump light with a periodic intensity distribution in the time domain or with periodic SBS threshold modulation capability. This Brillouin pump light is then used to periodically trigger stimulated Brillouin scattering within the gain fiber, ultimately generating and outputting periodically backpropagating Stokes pulses. The method provided in this application achieves precisely controllable pulse repetition frequency and narrow linewidth and pulse width characteristics, offering a practical SBS pulsed laser solution for fields with high requirements for timing accuracy and system stability.

[0079] In the foregoing descriptions of the embodiments, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0080] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

Claims

1. An all-fiber stimulated Brillouin scattering pulse generation device, characterized in that, include: A laser pumping module includes a seed source, a modulation structure, and a laser amplification system. The seed source is used to generate a seed laser, the modulation structure is used to modulate the seed laser, and the laser amplification system is used to amplify the modulated seed laser and use it as a Brillouin pump light. The Brillouin pump light has a periodic intensity distribution in the time domain or has a periodic SBS threshold modulation capability. A pulse generation module, connected to the laser pump module, includes a gain fiber; the pulse generation module is used to further amplify the Brillouin pump light and periodically trigger stimulated Brillouin scattering within the gain fiber to generate and output periodically backpropagating Stokes pulses.

2. The apparatus according to claim 1, characterized in that, The pulse generation module further includes a first isolator, a coupler, and a beam combiner connected in sequence, and a pump source connected to the beam combiner. The first isolator is disposed in the optical path between the coupler and the laser pump module to block the input of the back-propagating optical signal to the laser pump module. The beam combiner is disposed in the optical path between the gain fiber and the coupler and is connected to the pump source to combine the Brillouin pump light and the continuous pump light output by the pump source and output them to the gain fiber, and to output the back-propagating Stokes pulse to the coupler.

3. The apparatus according to claim 2, characterized in that, It also includes a pulse monitoring and feedback control module. The input terminal of the pulse monitoring and feedback module is connected to the pulse output terminal of the coupler, and is used to monitor the pulse parameters of the Stokes pulse light output by the coupler. The output terminal of the pulse monitoring and feedback module is connected to the laser pumping module and the pump source, and is used to feed back the modulation parameters and laser parameters of the Brillouin pump light based on the monitoring results. The pulse parameters of the Stokes pulse light include pulse shape, pulse repetition frequency, pulse width, and power parameters; the modulation parameters of the Brillouin pump light include modulation frequency, modulation period, duty cycle, modulation depth, and modulation bandwidth; the laser parameters of the Brillouin pump light include the seed source and the output power of the pump source.

4. The apparatus according to claim 1, characterized in that, The modulation structure includes a current control system connected to the seed source, which is used to output a rectangular modulation current signal to the seed source, so that the seed source generates the seed laser with rectangular intensity modulation. Alternatively, the modulation structure includes an electro-optic modulator, a radio frequency amplifier connected to the electro-optic modulator, and a signal generator connected to the radio frequency amplifier; wherein, The signal generator is used to generate and output modulated electrical signals; The radio frequency amplifier is used to receive the modulated electrical signal and amplify the modulated electrical signal before outputting it. The electro-optic modulator is connected to the seed source and the electro-optic modulator respectively, and is used to receive the seed laser output by the seed source and the modulated electrical signal after power amplification, and to perform intensity modulation or phase modulation on the seed laser based on the modulated electrical signal after power amplification.

5. The apparatus according to claim 4, characterized in that, The electro-optic modulator includes either an intensity modulator or a phase modulator; wherein... When the electro-optic modulator is the intensity modulator, the modulated electrical signal generated by the signal generator is a rectangular modulated electrical signal; In the case of the phase modulator, the modulated electrical signal generated by the signal generator is a continuously variable frequency electrical signal or a switching electrical signal that periodically switches between a constant electrical signal and a sinusoidal electrical signal, a white noise electrical signal, or a PRBS electrical signal.

6. The apparatus according to claim 4, characterized in that, When the pulse generation module receives Brillouin pump light with rectangular or intensity modulation, it will form periodically distributed illuminated and dark regions in the time domain within the gain fiber; wherein, The Brillouin pump light triggers stimulated Brillouin scattering in the illuminated region and generates periodically back-propagating Stokes pulses; the Brillouin pump light does not trigger stimulated Brillouin scattering in the dark region and does not generate periodically back-propagating Stokes pulses, and the light intensity of the Brillouin pump light in the illuminated region is greater than the light intensity in the dark region. Alternatively, when the pulse generation module receives a phase-modulated Brillouin pump, it will form a first region and a second region that are periodically distributed in the time domain within the gain fiber; wherein... The Brillouin pump light triggers stimulated Brillouin scattering in the first region and generates periodically back-propagating Stokes pulses; the Brillouin pump light does not trigger stimulated Brillouin scattering in the second region and does not generate periodically back-propagating Stokes pulses, and the SBS threshold corresponding to the first region is lower than the SBS threshold corresponding to the second region.

7. A method for generating stimulated Brillouin scattering pulses in an all-fiber optic cable, characterized in that, include: A seed laser and a modulation signal are provided. The seed laser is modulated using the modulation signal and amplified to serve as a Brillouin pump light. The Brillouin pump light has a periodic intensity distribution in the time domain or has a periodic SBS threshold modulation capability. The Brillouin pump light is further amplified and periodically triggered by the Brillouin pump light to generate and output periodically backpropagating Stokes pulses.

8. The method according to claim 7, characterized in that, The step of modulating the seed laser using the modulation signal and amplifying it to serve as the Brillouin pump light includes: A rectangular modulated current signal is output to the seed source using a current control system. The seed source is made to generate a seed laser with rectangular intensity modulation by using a rectangular modulation current signal; The seed laser, whose intensity is rectangularly modulated, is output to a laser amplification system for amplification, forming the Brillouin pump light with a periodic intensity distribution in the time domain.

9. The method according to claim 7, characterized in that, The step of modulating the seed laser using the modulation signal and amplifying it to serve as the Brillouin pump light includes: A rectangular modulated electrical signal is generated and output using a signal generator; The rectangular modulated electrical signal is amplified using a radio frequency amplifier; The intensity modulator receives the seed laser and the power-amplified rectangular modulation electrical signal, and performs rectangular modulation on the light intensity of the seed laser based on the power-amplified rectangular modulation electrical signal; The seed laser, after undergoing rectangular intensity modulation, is output to a laser amplification system for amplification, forming the Brillouin pump light with a periodic intensity distribution in the time domain.

10. The method according to claim 7, characterized in that, The step of modulating the seed laser using the modulation signal and amplifying it to serve as the Brillouin pump light includes: A signal generator is used to generate and output continuously variable frequency electrical signals or periodically switching electrical signals; The power of the continuously variable frequency electrical signal or the periodically switched electrical signal is amplified using a radio frequency amplifier; The phase of the seed laser is modulated based on the power-amplified continuous frequency conversion electrical signal or the periodically switched switching electrical signal, using a phase modulator to receive the seed laser and the power-amplified continuous frequency conversion electrical signal or the periodically switched switching electrical signal. The phase-modulated seed laser is output to a laser amplification system for amplification, forming the Brillouin pump light that can generate a periodic SBS threshold distribution in the gain fiber in the time domain.

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