Multi-channel time-coordinated pumped pulsed fiber laser amplifier

Abstract

The application provides a kind of multi-channel time sequence cooperative pumping pulse fiber laser amplifier, including single-frequency seed source, pulse pre-shaping module, pre-amplification module, main amplification stage module and monitoring module;Main amplification stage module includes at least two main amplification stage pumping channels, by independently controlling the pump accumulation time of each main amplification stage pumping channel, each main amplification stage pumping channel is segmented or overlapped in time domain with different pump accumulation time to the main gain fiber, so that the subsequent main amplification stage pumping channel is delayed and the pump accumulation time is shortened, the invalid high gain formed before the signal pulse arrives is reduced by the newly added pump energy, so as to suppress the ASE amplification caused by the shortening of ASE establishment time due to the increase of pump power and output signal power, the newly added pump energy can be mainly distributed in the signal pulse amplification window, so that higher pump energy can be more directly extracted by effective signal in subsequent amplification, and the energy utilization rate of main amplification stage is improved.

Description

Technical Field

[0001] This invention belongs to the field of laser technology, and in particular relates to a multi-channel time-sequentially pumped pulsed fiber laser amplifier. Background Technology

[0002] Fiber laser amplifiers (FLABs) possess advantages such as compact structure, strong heat dissipation, high conversion efficiency, good beam quality, easy fiber integration, and low maintenance costs, and have been widely used in fields such as lidar, coherent detection, optical communication, spectral measurement, precision machining, nonlinear frequency conversion, and beam combining. Existing high-power fiber laser systems typically employ a master oscillator power amplification structure, where a seed light with specific frequency, linewidth, or time-domain characteristics is generated by a pre-stage seed source, followed by multiple stages of pre-amplification and a master amplification stage to progressively increase power. This structure can achieve high-efficiency power amplification while maintaining the spectral and frequency characteristics of the seed source. However, under conditions of low repetition frequency, microsecond to millisecond-level long pulses, and high peak power, the master amplification stage accumulates a high population inversion before the pulse arrives. The signal pulse significantly extracts and consumes this inversion. The rate at which the gain is consumed at the beginning of the pulse exceeds the rate at which the pump replenishes the inversion, causing the instantaneous gain within the pulse to decrease over time. This results in high amplification at the beginning but insufficient amplification at the end, leading to a forward shift, spiked peaks, or a decrease in the flatness of the output pulse. Therefore, the performance improvement of long-pulse fiber laser amplification systems depends not only on amplification efficiency but also on the timing relationship between the pump injection, population inversion establishment, and signal light extraction processes of the main amplification stage. When the signal pulse arrives, the gain medium needs to have sufficient population inversion to ensure effective amplification of the pulse energy; however, if too much inversion accumulates before the signal arrives, or if a high level of unextracted inversion remains after the signal ends, the gain will be unevenly distributed in the time domain, further aggravating pulse waveform distortion and also providing conditions for the amplification of spontaneous emission noise.

[0003] To address the aforementioned issues, existing technologies typically employ seed pulse pre-shaping to compensate for time-domain waveform distortion caused by gain saturation, or synchronous pulse pumping to reduce ineffective pump injection within the pulse interval. By increasing seed light power to enhance signal light extraction of inverted particle number, shortening the gain fiber, or optimizing doping concentration and pump absorption coefficient to reduce ineffective gain accumulation, and filtering out the generated amplified spontaneous emission (ASE) component, these methods can improve the output waveform and signal-to-noise ratio to a certain extent. For low-repetition-frequency long-pulse amplification, the interval between adjacent signal pulses is relatively long, resulting in a lack of effective signal extraction in the gain medium for an extended period. If continuous pumping is used, the pump light continues to inject within the pulse interval, easily causing spontaneous emission to be amplified in a high-gain state without effective signal competition, thereby increasing the ASE component and reducing the signal-to-noise ratio of the signal spectrum. Synchronous pulse pumping, by concentrating the pump injection within the time range relevant to signal amplification, can reduce ineffective pump injection within the pulse interval and has a positive effect on suppressing ASE. However, for long pulses in the microsecond to millisecond range, the conversion of pump energy into population inversion requires a certain settling time, and the signal light continuously extracts inversions throughout the pulse's duration. Therefore, the width, energy, and delay time of the pump pulse need to be matched with the inversion settling and signal extraction processes. If the pump injection is insufficient or too late, the signal front will not receive sufficient gain; if the pump injection is too early, too strong, or too long, it will increase the proportion of no-signal or weak-signal amplification, thereby exacerbating ASE amplification and pulse waveform distortion. Therefore, the key to ASE suppression is to extract the available gain from the pump as effectively as possible to minimize the amplification of spontaneous emission noise by ineffective inversions.

[0004] Furthermore, when the output energy is further increased, the pump power usually needs to be increased accordingly, which shortens the settling time of the amplification assemblies (ASE) in the amplifier. If the additional pump energy is still provided by a single pump pulse within the same time window, the time distribution of the pump settling gain is difficult to match with the actual amplification process of long pulse signals, which can easily cause ASE to build up earlier before the arrival of the effective signal, and in severe cases, may even induce parasitic oscillations. Therefore, it is necessary to allocate the pump energy of the main amplification stage more finely in the time domain, so that the gain is mainly formed and consumed in the effective signal amplification stage, thus ensuring efficient pulse amplification while suppressing ASE caused by premature pump accumulation. Summary of the Invention

[0005] To address the technical problems existing in the prior art, the present invention provides a multi-channel time-sequentially pumped pulsed fiber laser amplifier.

[0006] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows: This invention provides a multi-channel time-coordinated pumped pulsed fiber laser amplifier, comprising: A single-frequency seed source is used to generate continuous single-frequency seed light; The pulse pre-shaping module is used to modulate continuous single-frequency laser into pre-shaped pulse single-frequency laser; The pre-amplification module is used to pre-amplify the power of pulsed single-frequency laser; The main amplification stage module includes at least one main amplifier, a main gain fiber, a multi-arm pump / signal combiner, and at least two main amplification stage pump channels for main power amplification of the pulsed single-frequency laser after power pre-amplification. Its signal end is the laser output port. The multiple main amplification stage pump channels inject high-power multimode pump light into the main gain fiber through the multi-arm pump / signal combiner. The monitoring module is located on the output optical path after the laser output port and is used to monitor the output laser parameters. The timing control module for the pump channel of the main amplifier stage controls the pump parameters of each pump channel in the main amplifier stage module. The pump parameters include trigger phase, pump accumulation time, pump duty cycle, pump pulse width, and pump energy. The moment when the pre-amplified pulsed single-frequency laser enters the main amplification stage module is denoted as . t 0, the pump start time of one or more main amplifier stage pump channels to be activated is recorded as . t i The current pump accumulation time is defined as follows: τ i =| t 0- t i | The pump accumulation time of each channel's activation is independently controlled by the main amplifier stage pump channel timing control module. This allows different main amplifier stage pump channels to inject pump light into the main gain fiber in segments or overlaps with different pump accumulation times in the time domain. At least two channels have different pump accumulation times when they are activated. This results in the delayed triggering of the currently activated subsequent main amplifier stage pump channel relative to all the activated preceding main amplifier stage pump channels, so that the newly added pump energy is mainly distributed within the effective amplification window of the pulsed single-frequency laser.

[0007] Compared with the prior art, the beneficial effects of this invention are as follows: (1) The present invention splits the total pump power of the main amplification stage into multiple independently controllable pump channels of the main amplification stage, so that the population inversion is no longer established excessively at once before the signal light arrives, thereby significantly reducing the risk of pre-signal ASE and parasitic oscillation.

[0008] (2) Furthermore, by delaying the triggering of the pump channel of the subsequent main amplification stage and shortening the pump accumulation time, the present invention reduces the formation of invalid high gain of the new pump energy of the subsequent main amplification channel before the arrival of the signal pulse, thereby suppressing the ASE amplification caused by the shortening of the ASE settling time due to the increase of pump power and output signal power. It can allocate the new pump energy mainly to the signal pulse amplification window, so that the higher pump energy can be extracted more directly by the effective signal in the subsequent amplification, thereby improving the energy utilization rate of the main amplification stage.

[0009] (3) The present invention can solve the problem of accelerated ASE establishment caused by synchronous pumping in-phase superposition amplification and improve the power expansion capability of the main amplification stage.

[0010] (4) This invention is not limited to single-frequency lasers, but can be applied to quasi-continuous and ordinary high-power pulse fiber amplification systems, and has strong versatility.

[0011] (5) This invention can be combined with forward spectrum, backward power, backward ASE, backward SBS and pulse flatness monitoring to form closed-loop control and improve the stability of the system under different pump power, different repetition frequency and different signal pulse width. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a schematic diagram of the framework structure of the multi-channel timing-coordinated pumped pulsed fiber laser amplifier of the present invention; Figure 2 This is a schematic diagram of the optical path structure of a multi-channel time-coordinated pumped pulsed fiber laser amplifier in one embodiment. Explanation of the labels in the diagram: 1. Single-frequency seed source; 2. Pulse pre-shaping module; 2-1. Acousto-optic modulator; 2-2. Arbitrary waveform generator; 3. Pre-amplification module; 3-1. First pre-amplifier; 3-2. Second pre-amplifier; 3-3. Third pre-amplifier; 3-4. Pre-amplification pump control module; 4. Main amplifier stage module; 4-1. First pump channel of main amplifier stage; 4-2. Second pump channel of main amplifier stage; 4-N. Nth pump channel of main amplifier stage; 5. Monitoring Module; 5-1. Circulator; 5-2. Spectrum Monitoring Unit; 5-3. Power Monitoring Unit; 5-4. Pulse Waveform Monitoring Unit; 6. Main amplifier stage pump channel timing control module. Detailed Implementation

[0013] The technical solution of the present invention will now be clearly and completely described through specific embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0014] Reference Figure 1 This embodiment provides a multi-channel time-coordinated pumped pulsed fiber laser amplifier, comprising: Single-frequency seed source 1 is used to generate continuous single-frequency seed light; Pulse pre-shaping module 2 is used to modulate continuous single-frequency laser into pre-shaped pulsed single-frequency laser; Pre-amplification module 3 is used to pre-amplify the power of pulsed single-frequency laser; The main amplification stage module 4 includes at least one main amplifier, a main gain fiber, a multi-arm pump / signal combiner, and at least two main amplification stage pump channels for main power amplification of the pre-amplified pulsed single-frequency laser. Its signal end is the laser output port. The multiple main amplification stage pump channels inject high-power multimode pump light into the main gain fiber through the multi-arm pump / signal combiner. Preferably, the main gain fiber is a polarization-maintaining large-mode-field tapered ytterbium-doped fiber.

[0015] Monitoring module 5 is installed in the output optical path after the laser output port to monitor the output laser parameters; The main amplifier stage pump channel timing control module 6 controls the pump parameters of each pump channel in the main amplifier stage module 4. The pump parameters include trigger phase, pump accumulation time, pump duty cycle, pump pulse width, pump energy, pump waveform, etc. The moment when the pre-amplified pulsed single-frequency laser enters the main amplification stage module is denoted as . t 0, the pump start time of one or more main amplifier stage pump channels to be activated is recorded as . t i The current pump accumulation time is defined as follows: τ i =| t 0- t i |The pump accumulation time of each channel's activation is independently controlled by the main amplifier stage pump channel timing control module. This allows different main amplifier stage pump channels to inject pump light into the main gain fiber in segments or overlaps with different pump accumulation times in the time domain. At least two channels have different pump accumulation times when they are activated. This results in the delayed triggering of the currently activated subsequent main amplifier stage pump channel relative to all the activated preceding main amplifier stage pump channels, so that the newly added pump energy is mainly distributed within the effective amplification window of the pulsed single-frequency laser.

[0016] It is important to clarify that in each activation action, all previously activated main amplifier stage pump channels are collectively referred to as preceding channels, the channels currently being activated are called subsequent channels, and the remaining untriggered channels are called inactive channels. Here, the main amplifier stage pump channels are categorized only by three real-time states: activated, currently activated, and inactive. Furthermore, each activation action is an incremental trigger, meaning only the channel currently being activated is added, while all already activated preceding channels are not shut down, maintaining their continuous pumping state. This achieves a stepwise increase in total pump power until all channels are activated. Furthermore, the timing control module 6 of the main amplification stage pump channel uses the time window of the pulsed single-frequency laser (signal light) entering the main amplification stage module 4 as a reference. Based on the amplification degree of the signal pulse already completed by the preceding main amplification stage pump channel and the ASE establishment trend, it controls the subsequent main amplification stage pump channel to simultaneously shorten the pump accumulation time of the subsequent main amplification stage pump channel while increasing the total pump power. This limits the new pump energy to the amplification window in which the signal pulse can effectively extract gain, avoiding ASE extraction of gain. The pump start time of the preceding main amplification stage pump channel is earlier than the pump start time of the subsequent main amplification stage pump channel.

[0017] Specifically, the additional pump energy is limited to the amplification window within which the signal pulse can effectively extract gain, achieved in the following way: The main amplifier stage pump channel timing control module 6 simulates and calculates the impact of the pump accumulation time of the subsequent main amplifier stage pump channel on the output signal power and the ASE power before and after the signal pulse, based on the amplification degree of the signal pulse completed by the preceding main amplifier stage pump channel and the ASE establishment trend, so as to realize the control of the pump accumulation time of the subsequent main amplifier stage pump channel.

[0018] Reference Figure 2One embodiment provides a multi-channel timing-coordinated pumped pulsed fiber laser amplifier, including a single-frequency seed source 1, an acousto-optic modulator 2-1, an arbitrary waveform generator 2-2, a first preamplifier 3-1, a second preamplifier 3-2, a third preamplifier 3-3, a preamplification pump control module 3-4, a main amplification stage module 4, a first pump channel 4-1 of the main amplification stage, a second pump channel 4-2 of the main amplification stage, a circulator 5-1, a spectral monitoring unit 5-2, a power monitoring unit 5-3, a pulse waveform monitoring unit 5-4, and a main amplification stage pump channel timing control module 6. In the figure, the arbitrary waveform generator 2-2, the preamplification pump control module 3-4, and the main amplification stage pump channel timing control module 6 are arranged together; in practical applications, they can be set up independently or integrated together.

[0019] After the pulse pre-shaping module 2 is connected to the single-frequency seed source 1, in this embodiment, the pulse pre-shaping module 2 includes an acousto-optic modulator 2-1 and an arbitrary waveform generator 2-2. The acousto-optic modulator 2-1 is used to receive the continuous single-frequency laser output from the single-frequency seed source 1. The arbitrary waveform generator 2-2 is connected to the acousto-optic modulator 2-1 and is used to generate a modulation drive signal to modulate the continuous single-frequency laser into a pre-shaped pulse single-frequency laser.

[0020] The pre-amplification stage module 3 includes a first pre-amplifier 3-1, a second pre-amplifier 3-2, and a third pre-amplifier 3-3 connected in sequence, used to amplify the pre-shaped pulsed single-frequency laser step by step. Furthermore, the pre-amplification stage module 3 also includes a pre-amplification pump control module 3-4, which is connected to the pump sources in each pre-amplification stage of the pre-amplification module 3, and is used to independently control the pump parameters of the pump sources in each pre-amplification stage.

[0021] The main amplification stage module 4 includes N main amplification stage pump channels, namely, the first pump channel 4-1, the second pump channel 4-2, ..., the Nth pump channel 4-N. Furthermore, to achieve more refined pump timing control, the number of main amplification stage pump channels can be increased, with N being greater than or equal to 2. All main amplification stage pump channels are independently controlled by the main amplification channel timing control module 6.

[0022] The monitoring module 5 includes a circulator 5-1 and one or more monitoring units among the following: a spectrum monitoring unit 5-2, a power monitoring unit 5-3, and a pulse waveform monitoring unit 5-4. It is capable of monitoring the output spectrum, backlight, ASE component, SBS component, and / or the output pulse waveform.

[0023] The circulator 5-1 is disposed between the pre-amplification stage module 3, which includes a multi-stage pre-amplifier, and the main amplification stage module 4, and is used to block or monitor the backscattered light generated by the main amplification stage; The spectral monitoring unit 5-2 is used to monitor the ASE component and the SBS backlight spectrum; The power monitoring unit 5-3 is used to monitor the output power or the backlight power. The pulse waveform monitoring unit 5-4 is used to monitor the time-domain waveform of the output pulse; The monitoring results of the monitoring module 5 are used to provide feedback on the pulse pre-shaping parameters in the pulse pre-shaping module 2, the pumping parameters of the pump sources in each stage of the pre-amplification stage in the pre-amplification stage module 3, and the pumping timing parameters of each pump channel in the main amplification stage in the main amplification stage pump channel timing control module 6.

[0024] For the two main amplification stage pump channels, either the first pump channel 4-1 or the second pump channel 4-2 of the main amplification stage is activated first. The pump channel activated first is the preceding main amplification stage pump channel, and the pump channel activated later is the subsequent main amplification stage pump channel. The main amplification stage pump channel timing control module 6 uses the time window when the signal pulse enters the main amplification stage module 4 as a reference. Based on the signal amplification degree and ASE establishment trend of the preceding main amplification stage pump channel, it controls the subsequent main amplification stage pump channel to simultaneously shorten the pump accumulation time while increasing the total pump power, thus limiting the newly added pump energy mainly within the amplification window of the effective extraction gain of the signal pulse. The main amplification stage pump channel timing control module 6 shuts down all main amplification stage pump channels at the end of the signal pulse, thereby suppressing ASE accumulation caused by the accelerated ASE establishment speed and shortened establishment time under conditions of increased pump power and signal power, and improving the energy extraction efficiency and signal-to-noise ratio of the main amplification stage module. This invention is applicable to fiber optic main amplification systems that require high signal-to-noise ratio amplification, such as single-frequency and narrow-linewidth systems. It is particularly suitable for fiber optic amplification scenarios with low repetition frequency, long pulses with high peak power and high energy at pulse widths in the range of hundreds of microseconds to milliseconds.

[0025] The above embodiment is illustrated using two main amplifier stage pump channels (one in front of the other). However, in practical applications, the number of main amplifier stage pump channels can be increased. The number of main amplifier stage pump channels is not limited to two and can be expanded to more than two as needed. In the case of having more than two main amplifier stage pump channels, the start-up of each main amplifier stage pump channel is also independently controlled by the amplifier pump channel timing control module 6.

[0026] In the initial stage, the amplification pump channel timing control module 6 can first activate one or more main amplification stage pump channels. Subsequent activation operations are based on the time window when the signal pulse enters the main amplification stage module 4, and combined with the signal amplification degree and amplified spontaneous emission (ASE) establishment trend of the previously activated channels, controlling the subsequent channels to increase the total pump power while simultaneously shortening the pump accumulation time, thereby mainly constraining the newly added pump energy (i.e., the pump energy added by activating the subsequent channels) within the amplification window of the effective extraction gain of the signal pulse. It should be noted that the number of channels activated in subsequent batches is not fixed and can be flexibly determined according to the actual operating conditions, and is not limited to activating only one at a time. In addition, for the channel to be activated, all previously activated channels are considered its predecessor channels; the distinction between "predecessor" and "subsequent" is based on the currently activated channels to distinguish between the activated group and the group to be activated, and both are phased concepts.

[0027] In one embodiment, the single-frequency seed source 1 is a continuous single-frequency laser seed source with a center wavelength of 1064 nm and a beamwidth of 260 Hz. The pulse pre-shaping module 2 includes an acousto-optic modulator 2-2 and a multi-channel arbitrary waveform generator 2-2. The acousto-optic modulator 2-1 is used to modulate the intensity of the continuous single-frequency seed light, and the multi-channel arbitrary waveform generator 2-2 provides synchronous drive signals to the acousto-optic modulator 2-1 and each stage of the pre-amplification stage in the pre-amplification stage module 3. The acousto-optic modulator 2-1 modulates the continuous single-frequency seed light output from the single-frequency seed source 1 into a pre-shaped pulsed single-frequency laser with a repetition frequency of 100Hz and a full pulse width of 800μs. The temporal intensity of the pre-shaped pulsed single-frequency laser includes a linear rise segment from 0μs to 196.3μs, an exponential rise segment from 196.3μs to 750μs, and an inverse exponential decay segment from 750μs to 800μs. This is used to compensate for the over-amplification of the leading edge caused by gain saturation during subsequent amplification, so that the output pulse gradually evolves into a quasi-rectangular pulse.

[0028] The multi-stage pre-amplification module 3 is connected after the pulse pre-shaping module 2, and includes a first pre-amplifier 3-1, a second pre-amplifier 3-2, and a third pre-amplifier 3-3 connected in sequence. The first and second pre-amplifiers 3-1 and 3-2 respectively use single-mode ytterbium-doped fiber as the gain fiber and are connected to 976 nm single-mode pump light through a pump / signal wavelength division multiplexer; the third pre-amplifier 3-3 uses double-clad ytterbium-doped fiber as the gain fiber and is connected to 976 nm multi-mode pump light through a pump / signal combiner. The pump source of each pre-amplifier is independently controlled by the multi-channel arbitrary waveform generator 2-2 to match the gain establishment during each pre-amplification process with the transmission timing of the pre-shaped pulsed single-frequency laser. That is, in this embodiment, the multi-channel arbitrary waveform generator 2-2 also serves as the pre-amplification pump control module 3-4. The multi-channel arbitrary waveform generator 2-2 performs graded control of the pump source of each stage of the preamplifier, so that the pump pulse of the preamplifier stage is matched with the pre-shaping signal pulse in time, thereby taking into account both gain saturation compensation and ASE suppression during the preamplification process.

[0029] Furthermore, filters are installed after each preamplifier stage to remove the ASE component generated during the preamplification process; fiber optic isolators are installed between adjacent amplification stages to suppress the influence of backscattered light on the optical path of the preceding stage.

[0030] The main amplification stage module 4 is connected after the multi-stage pre-amplification module 3. In this embodiment, two main amplification stage pump channels are used as an example for illustration. All main amplification stage pump channels are independently controlled by the main amplification channel timing control module 6. The main amplification stage module 4 includes a polarization-maintaining large-mode-field tapered ytterbium-doped gain fiber, a pump / signal combiner, and two independently controlled 976 nm multimode pump channels, namely the first pump channel 4-1 and the second pump channel 4-2. The polarization-maintaining large-mode-field tapered ytterbium-doped gain fiber has a cladding absorption coefficient of 10 dB / m at 976 nm, a narrow-end core / inner cladding diameter of 35 / 250 μm, and a wide-end core / inner cladding diameter of 56 / 400 μm. The polarization-maintaining large-mode-field tapered ytterbium-doped gain fiber includes a narrow end section, a tapered transition section, and a wide end section, wherein the narrow end section is 0.1 m long, the tapered transition section is 0.7 m long, and the wide end section is 1.3 m long. The pump / signal combiner is a (2+1)×1 pump / signal combiner, with its signal and output ends using fiber with a core / cladding diameter of 25 / 250 μm to facilitate low-loss fusion splicing with the narrow end of the tapered gain fiber and maintain output beam quality. The fiber optic devices in the main amplification stage are mounted on a water-cooled plate to improve system heat dissipation and long-term operational stability.

[0031] In this embodiment, the first pump channel 4-1 and the second pump channel 4-2 of the main amplification stage are turned on sequentially, with the first one being the preceding main amplification stage pump channel and the second one being the subsequent main amplification stage pump channel. The moment when the signal pulse enters the main amplification stage module 4 is recorded as... t 0, will the first i The pump start time of each main amplifier stage pump channel is denoted as t i Then the first i The pump accumulation time of each main amplifier stage pump channel relative to the signal pulse is defined as... τ i =| t 0- t i | The timing control module 6 for the pump channels of the main amplification stage controls the trigger phase, pump duty cycle, pump peak power, and pump accumulation time of each pump channel in the main amplification stage, enabling each pump channel to inject pump light into the main gain fiber in segments or overlaps within the time domain. Through this method, the pump energy in the main amplification stage module is no longer injected all at once by a single pump pulse, but rather distributed in the time domain according to the amplification process of the signal pulse in the main amplification stage module, ensuring that the effective gain is mainly formed within the time window during which the signal pulse can extract gain.

[0032] In this embodiment, as the total pump power of the main amplification stage increases, if each pump channel of the main amplification stage uses the same pump accumulation time, the small-signal gain before the signal pulse arrives increases, the ASE setup time is shortened, and it is easy to cause ASE enhancement before the signal. By delaying the triggering of the subsequent pump channel of the main amplification stage relative to the preceding pump channel to shorten the pump accumulation time, more of the newly added pump energy can be allocated to the signal pulse amplification window, thereby suppressing ASE amplification before the signal and improving the signal energy extraction efficiency. Preferably, the first pump channel 4-1 of the main amplification stage is turned on first. The first pump channel 4-1 of the main amplification stage is used to establish the basic gain to provide amplification. The subsequent pump channel of the main amplification stage (the second pump channel 4-2 of the main amplification stage) is used to supplement the gain during the signal pulse amplification process, and ASE is suppressed by optimizing the pump accumulation time.

[0033] The monitoring module 5 includes a circulator 5-1, a spectral monitoring unit 5-2, a power monitoring unit 5-3, and a pulse waveform monitoring unit 5-4. The circulator 5-1 is positioned between the multi-stage pre-amplification module 3 and the main amplification stage module 4 to block or monitor the backscattered light returned from the main amplification stage. The spectral monitoring unit 5-2 monitors the forward output spectrum, the backward ASE spectrum, and the backward SBS spectrum. The power monitoring unit 5-3 monitors the output peak power and the backward return power. The pulse waveform monitoring unit 5-4 includes a photodetector and a digital oscilloscope to monitor the evolution of the pulse time-domain waveform during amplification. The monitoring results from the monitoring feedback module 5 are used to adjust the seed pulse pre-shaping waveform, the pump timing of each pre-amplification stage, and the pump phase, pump pulse duty cycle, and pump power of each pump channel in the main amplification stage.

[0034] In this embodiment, when the pump peak power injected into the main amplification stage module 4 is 621.5 W, the peak power of the amplified pulsed single-frequency laser output reaches 505 W, with a slope efficiency of 81.26%. Under the condition of maximum output peak power, no obvious ASE component was observed in the forward output spectrum, and the spectral signal-to-noise ratio was approximately 60.71 dB; the beam quality factor M² was approximately 1.24 at the output peak power of 505 W; the polarization extinction ratio at the maximum output peak power was 15 dB; the root mean square ripple was less than 0.44% in the 1-hour power stability test; and the amplitude standard deviation of 10,000 consecutive pulses was approximately 2.62%, indicating that the amplifier can achieve high peak power, high signal-to-noise ratio, near-diffraction-limited beam quality, and stable linear polarization output.

[0035] In this embodiment, the amplified pulsed single-frequency laser forms a quasi-rectangular pulse at maximum output peak power, with a full width at half maximum (FWHM) of 567 μs and a repetition frequency of 100 Hz. No parasitic pulses were observed in the pulse sequence. The formation of the quasi-rectangular pulse is due to the combined effect of seed pulse pre-shaping and multi-stage synchronous pump timing control: seed pulse pre-shaping is used to compensate for the over-amplification at the leading edge and under-amplification at the trailing edge caused by gain saturation, while multi-stage main amplification pumping is used to provide a matched gain window during the effective amplification stage of the signal pulse, suppressing ASE amplification, improving pulse flatness, and maintaining high pulse contrast.

[0036] In summary, this embodiment combines pulse pre-shaping with multi-channel timing-coordinated pumping, ensuring that the additional pump energy in the main amplification stage is primarily distributed within the effective amplification window of the signal pulse. This suppresses the ASE amplification problem caused by the shortened ASE settling time as pump power increases. Simultaneously, the use of polarization-maintaining large-mode-field tapered ytterbium-doped gain fiber improves the SBS threshold and maintains good beam quality. The device models, pump power, pulse width, fiber size, and number of pump channels described in this embodiment are merely preferred examples and do not constitute a limitation on the scope of protection of this invention. Any equivalent substitutions, simple modifications, or combinations made to the number of pump channels, pump wavelength, gain fiber size, pre-shaping waveform, synchronization timing parameters, or monitoring feedback methods without departing from the technical principles of this invention should fall within the scope of protection of this invention.

[0037] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

[0038] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multi-channel time-sequentially pumped pulsed fiber laser amplifier, characterized in that, include: A single-frequency seed source is used to generate continuous single-frequency seed light; The pulse pre-shaping module is used to modulate continuous single-frequency laser into pre-shaped pulse single-frequency laser; The pre-amplification module is used to pre-amplify the power of pulsed single-frequency laser; The main amplification stage module includes at least one main amplifier, a main gain fiber, a multi-arm pump / signal combiner, and at least two main amplification stage pump channels for main power amplification of the pulsed single-frequency laser after power pre-amplification. Its signal end is the laser output port. The multiple main amplification stage pump channels inject high-power multimode pump light into the main gain fiber through the multi-arm pump / signal combiner. The monitoring module is located on the output optical path after the laser output port and is used to monitor the output laser parameters. The timing control module for the pump channel of the main amplifier stage controls the pump parameters of each pump channel in the main amplifier stage module. The pump parameters include trigger phase, pump accumulation time, pump duty cycle, pump pulse width, pump energy, and pump waveform. The moment when the pre-amplified pulsed single-frequency laser enters the main amplification stage module is denoted as . t 0, the pump start time of one or more main amplifier stage pump channels to be activated is recorded as . t i The current pump accumulation time is defined as follows: τ i =| t 0- t i | The pump accumulation time of each channel's activation is independently controlled by the main amplifier stage pump channel timing control module. This allows different main amplifier stage pump channels to inject pump light into the main gain fiber in segments or overlaps with different pump accumulation times in the time domain. At least two channels have different pump accumulation times when they are activated. This results in the delayed triggering of the currently activated subsequent main amplifier stage pump channel relative to all the activated preceding main amplifier stage pump channels, so that the newly added pump energy is mainly distributed within the effective amplification window of the pulsed single-frequency laser.

2. The multi-channel time-sequentially pumped pulsed fiber laser amplifier according to claim 1, characterized in that, The timing control module of the main amplification stage pump channel uses the time window of the pulsed single-frequency laser entering the main amplification stage module as a reference. Based on the amplification degree of the signal pulse completed by the preceding main amplification stage pump channel and the ASE establishment trend, it controls the subsequent main amplification stage pump channel to simultaneously shorten the pump accumulation time of the subsequent main amplification stage pump channel while increasing the total pump power. This limits the new pump energy to the amplification window in which the signal pulse can effectively extract gain, avoiding ASE extraction of gain. The pump start time of the preceding main amplification stage pump channel is earlier than the pump start time of the subsequent main amplification stage pump channel.

3. The multi-channel time-sequentially pumped pulsed fiber laser amplifier according to claim 2, characterized in that, By controlling the pump timing of the multi-channel main amplifier stage, the subsequent additional pump energy is limited to the amplification window where the signal pulse can effectively extract gain. This is achieved through the following method: The main amplifier stage pump channel timing control module simulates and calculates the impact of the pump accumulation time of the subsequent main amplifier stage pump channel on the output signal power and the ASE power before and after the signal pulse, based on the amplification degree of the signal pulse completed by the preceding main amplifier stage pump channel and the ASE establishment trend, so as to realize the control of the pump accumulation time of the subsequent main amplifier stage pump channel.

4. The multi-channel time-sequentially pumped pulsed fiber laser amplifier according to claim 1, 2, or 3, characterized in that, The pulse pre-shaping module is connected after the single-frequency seed source and includes an acousto-optic modulator and an arbitrary waveform generator. The acousto-optic modulator is used to receive the continuous single-frequency laser output from the single-frequency seed source. The arbitrary waveform generator is connected to the acousto-optic modulator and is used to generate a modulation drive signal to modulate the continuous single-frequency laser into a pre-shaped pulsed single-frequency laser.

5. The multi-channel time-sequentially pumped pulsed fiber laser amplifier according to claim 4, characterized in that, It also includes a pre-amplification pump control module, which is connected to the pump source in each pre-amplification stage of the pre-amplification module and is used to independently control the pump parameters of the pump source in each pre-amplification stage.

6. The multi-channel time-sequentially pumped pulsed fiber laser amplifier according to claim 5, characterized in that, The pre-amplification stage module includes a first pre-amplifier, a second pre-amplifier, and a third pre-amplifier connected in sequence. The first and second pre-amplifiers respectively use single-mode ytterbium-doped fiber as the gain fiber and are connected to single-mode pump light through a pump / signal wavelength division multiplexer. The third pre-amplifier uses double-clad ytterbium-doped fiber as the gain fiber and is connected to multimode pump light through a pump / signal combiner. The pump source of each pre-amplifier is independently controlled by the pre-amplification pump control module to match the gain establishment during each pre-amplification process with the transmission timing of the pre-shaped pulsed single-frequency laser.

7. The multi-channel time-sequentially pumped pulsed fiber laser amplifier according to claim 1, 2, 3, 5, or 6, characterized in that, The main gain fiber is a polarization-maintaining large-mode-field tapered ytterbium-doped fiber.

8. The multi-channel time-sequentially pumped pulsed fiber laser amplifier according to claim 7, characterized in that, The monitoring module includes a circulator and one or more monitoring units selected from a spectrum monitoring unit, a power monitoring unit, and a pulse waveform monitoring unit. The circulator is positioned between the multi-stage pre-amplification module and the main amplification stage module to block or monitor backscattered light generated by the main amplification stage. The spectral monitoring unit is used to monitor the ASE components and the stimulated Brillouin scattering back spectrum. The power monitoring unit is used to monitor the output power or the backlight power. The pulse waveform monitoring unit is used to monitor the time-domain waveform of the output pulse; The monitoring results of the monitoring module are used to provide feedback on the pulse pre-shaping parameters in the pulse pre-shaping module, the pumping parameters of the pump sources in each stage of the pre-amplification stage module, and the pumping timing parameters of each pump channel in the main amplification stage pump channel timing control module.

9. The multi-channel time-sequentially pumped pulsed fiber laser amplifier according to claim 1, 2, 3, 5, 6, or 8, characterized in that, The single-frequency seed source is a continuous single-frequency laser seed source with a center wavelength of 1064nm and a continuous single-frequency seed beam width of 260Hz.

10. The multi-channel time-sequentially pumped pulsed fiber laser amplifier according to claim 9, characterized in that, The acousto-optic modulator modulates the continuous single-frequency seed light output from the single-frequency seed source into a pre-shaped pulsed single-frequency laser with a repetition frequency of 100Hz and a full pulse width of 800μs. The temporal intensity of the pre-shaped pulsed single-frequency laser includes a linear rise segment from 0μs to 196.3μs, an exponential rise segment from 196.3μs to 750μs, and an inverse exponential decay segment from 750μs to 800μs. This is used to compensate for the leading-edge over-amplification caused by gain saturation during subsequent amplification, so that the output pulse gradually evolves into a quasi-rectangular pulse.

Images