Ultrahigh repetition frequency adjustable ultrashort pulse cluster generator

Abstract

The invention discloses an ultrahigh repetition frequency adjustable ultrashort pulse cluster generator which comprises a mode-locked fiber laser, a first fiber coupler, a fiber delay line, a dispersion compensation fiber, a second fiber coupler, a fiber amplifier and an acousto-optic modulator. The first optical fiber coupler, the optical fiber delay line, the dispersion compensation optical fiber, the second optical fiber coupler and the optical fiber amplifier are sequentially connected end to end to form an optical fiber annular cavity, and the annular cavity is used as a frequency increasing device for pulse multiplication; the length difference between the optical fiber annular cavity and a mode-locked cavity in the mode-locked optical fiber laser is adjusted through the optical fiber delay line, and frequency increasing is carried out by using a vernier effect generated by time delay; the ultrahigh repetition frequency ultrashort pulse cluster laser output with adjustable parameters is realized through gain adjustment in the optical fiber annular cavity and synchronous pulse pickup outside the cavity. According to the technical scheme, the structural design is reasonable, the structure is simple, stability is good, sub-pulses are strictly equidistant, parameters are flexible and adjustable, and practicability is good.

Description

Technical Field

[0001] The invention relates to the field of laser and optoelectronic technology, and in particular to an ultra-high repetition rate adjustable ultra-short pulse cluster generator. Background Art

[0002] Ultrashort pulse cluster laser refers to a pulse operation mode in which ultrashort pulses are stacked in the time domain to form a cluster structure. It plays an important role in many fields such as optical communication systems, precision material processing and scientific research. When using this pulse structure for material processing, it has the advantages of low ablation threshold, high cutting efficiency and low thermal damage. In other words, the pulse cluster structure formed by stacking multiple ultrashort pulses has a material ablation speed similar to that of a single pulse. Therefore, each cluster envelope can be regarded as a single high-energy pulse, which greatly reduces the dependence of material ablation on the energy of a single laser pulse.

[0003] The sub-pulse repetition frequency is a very important parameter of pulse cluster lasers. A higher repetition frequency corresponds to a smaller pulse interval, which can greatly improve material processing efficiency, reduce the ablation threshold, and reduce the heat-affected zone. In addition, high-repetition-rate pulse clusters can also help reduce the plasma shielding effect, thereby further improving the ablation efficiency.

[0004] Traditional pulse cluster acquisition schemes include laser intracavity dynamics control and extracavity time domain control. The former mainly utilizes the clamping effect of peak power and the repulsion between adjacent pulses to split a single pulse into multiple sub-pulses. Although the pulse cluster obtained by this method has a high sub-pulse repetition rate, its output power is limited and the pulse cluster repetition rate and the number of sub-pulses are relatively fixed, which cannot adapt to different application scenarios; in addition, this scheme is easily affected by the environment and pulse collapse occurs. Therefore, it is not the preferred scheme for obtaining pulse clusters. For extracavity time domain control technology, pulse cluster output is mainly achieved through pulse frequency boosting-picking. Due to the limitations of experimental schemes and process errors, this scheme is difficult to achieve ultra-high repetition rates exceeding the GHz level, and there are defects such as sub-pulse jitter and unstable repetition rate, which greatly limits the application scope of pulse cluster lasers. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide an ultra-high repetition rate adjustable ultrashort pulse cluster generator with reasonable structural design, simple structure, good stability, strictly equidistant sub-pulses, flexible and adjustable parameters and good practicality.

[0006] To achieve the above-mentioned purpose, the present invention provides the following technical solution: an ultra-high repetition rate adjustable ultra-short pulse cluster generator, comprising a mode-locked fiber laser, a first fiber coupler, a fiber delay line, a dispersion-compensating fiber, a second fiber coupler, a fiber amplifier and an acousto-optic modulator, wherein the first fiber coupler, the fiber delay line, the dispersion-compensating fiber, the second fiber coupler and the fiber amplifier are connected end to end in sequence to form a fiber ring cavity, and the ring cavity is used as a frequency multiplier for pulse multiplication; the first fiber coupler is used as an input port of the frequency multiplier, and the second fiber coupler is used as an output port of the frequency multiplier, and a baseband pulse signal is input from the first fiber coupler into the fiber ring cavity for frequency multiplication, and then the baseband pulse signal is multiplied from the first fiber coupler. The second fiber coupler outputs a frequency-increased pulse sequence; the fiber delay line is used to adjust the length difference between the fiber ring cavity and the mode-locked cavity in the mode-locked fiber laser, and the vernier effect is used to realize an ultra-high repetition rate ultra-short pulse sequence; the dispersion compensation fiber is used to compensate for the dispersion in the cavity to prevent pulse broadening; the fiber amplifier is used to balance the intra-cavity loss of the fiber ring cavity to eliminate the ring-down effect of the fiber ring cavity; the acousto-optic modulator is placed at the output end of the fiber ring cavity, and the mode-locked fiber laser is used for synchronous triggering. The acousto-optic modulator is used to pick up a pulse cluster laser with required parameters, and the output of an ultra-high repetition rate ultra-short pulse cluster laser with adjustable parameters is realized through the gain adjustment in the fiber ring cavity and the synchronous pulse picking outside the cavity.

[0007] The present invention is further configured as follows: the mode-locked fiber laser provides a trigger source and an initial base frequency pulse signal for the acousto-optic modulator, and its peak power is within 10W.

[0008] The present invention is further configured as follows: the input end of the first fiber coupler is connected to the mode-locked fiber laser, the isolation end of the first fiber coupler is connected to the output end of the fiber amplifier, the coupling end of the first fiber coupler is connected to the input end of the fiber delay line, the through end of the first fiber coupler is suspended, and the power coupled into the fiber ring cavity by the first fiber coupler is between 10% and 20%.

[0009] The present invention is further configured as follows: the output end of the optical fiber delay line is connected to the dispersion compensating optical fiber for finely adjusting the cavity length to achieve dense pulse frequency increasing. The delay range of the optical fiber delay line is 0-300ps, and the delay accuracy is within 1ps.

[0010] The present invention is further configured as follows: one end of the dispersion compensating optical fiber is connected to the output end of the optical fiber delay line, the other end of the dispersion compensating optical fiber is connected to the input end of the second optical fiber coupler, and the dispersion value of the dispersion compensating optical fiber is determined by the total dispersion of the optical fiber ring cavity.

[0011] The present invention is further configured as follows: the input end of the second fiber coupler is connected to the dispersion compensating fiber, the through end of the second fiber coupler is connected to the seed input end of the fiber amplifier, the coupling end of the second fiber coupler is connected to the input end of the acousto-optic modulator, and the isolation end of the second fiber coupler is suspended; while ensuring that the output signal strength is sufficient, the coupled output power of the fiber ring cavity is between 1% and 5%.

[0012] The present invention is further configured as follows: the optical fiber amplifier consists of three parts: a gain optical fiber, a wavelength division multiplexer, and a pump source; the doping ions of the gain optical fiber are determined by the initial pulse wavelength provided by the mode-locked optical fiber laser; the length of the gain optical fiber is determined by the total loss in the optical fiber ring cavity; and the pump source is a semiconductor laser.

[0013] The present invention is further configured such that the modulation wavelength range of the acousto-optic modulator matches the wavelength of the mode-locked fiber laser, and the rise / fall time thereof is less than 15ns, thereby ensuring that the frequency-reduced pulse has a pure spectrum.

[0014] The beneficial effects of the present invention are as follows: compared with the prior art, the present invention has a reasonable structural design, combines the pulse replication function of the fiber ring cavity with the vernier effect, and realizes dense pulse frequency increase; uses the fiber amplifier to compensate for the inherent loss of the ring cavity and solves its inherent ring-down effect. Further, through dispersion compensation, the pulse broadening and distortion caused by the accumulation of dispersion after multiple pulse replications are avoided, thereby realizing the output of a pulse sequence with strictly equidistant sub-pulses and ultra-high repetition rate; finally, through the pulse picking of the synchronous acousto-optic modulator, a pulse cluster laser mode with flexible parameter adjustment can be realized.

[0015] Compared with the traditional pulse cluster acquisition scheme, the present invention omits the complex intracavity dynamics control, does not have the sub-pulse spacing fluctuation caused by pulse collapse and process error, and breaks through the technical problem of limited repetition frequency. It is a technical solution for ultra-high repetition rate and ultra-short pulse cluster generator with good system stability, simple structure, low cost, and flexible and adjustable parameters, which overcomes the technical difficulties of limited repetition rate and unequal sub-pulse spacing in traditional schemes. It has broad application prospects and good practicality in the fields of precision material processing, optical communication systems and scientific research.

[0016] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of an embodiment of the present invention; Figure 2 This is a schematic diagram of the frequency enhancement of the optical fiber ring cavity according to an embodiment of the present invention. DETAILED DESCRIPTION

[0018] In the description of this embodiment, it should be noted that, if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", "front", "back", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore, cannot be understood as limiting the present invention. In addition, if the terms "first", "second", and "third" appear, they are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0019] See also Figure 1 to Figure 2 The present invention discloses an ultra-high repetition rate adjustable ultra-short pulse cluster generator, comprising a mode-locked fiber laser 1, a first fiber coupler 2, a fiber delay line 3, a dispersion compensating fiber 4, a second fiber coupler 5, a fiber amplifier 6 and an acousto-optic modulator 7. The first fiber coupler 2, the fiber delay line 3, the dispersion compensating fiber 4, the second fiber coupler 5 and the fiber amplifier 6 are connected end to end in sequence to form a fiber ring cavity, and the ring cavity is used as a frequency multiplier for pulse multiplication; the first fiber coupler 2 is used as an input port of the frequency multiplier, and the second fiber coupler 5 is used as an output port of the frequency multiplier. The base frequency pulse signal is input from the first fiber coupler 2 into the fiber ring cavity for frequency multiplication, and the second fiber coupler 5 is output from the second fiber coupler 2. The coupler 5 outputs a frequency-increased pulse sequence; the length difference between the optical fiber ring cavity and the mode-locked cavity in the mode-locked optical fiber laser 1 is adjusted by the optical fiber delay line 3, and an ultra-short pulse sequence with an ultra-high repetition rate is realized by using the vernier effect; the dispersion compensation optical fiber 4 is used to compensate for the dispersion in the cavity to prevent pulse broadening; the optical fiber amplifier 6 balances the intracavity loss of the optical fiber ring cavity to eliminate the ring-down effect of the optical fiber ring cavity; the acousto-optic modulator 7 is placed at the output end of the optical fiber ring cavity, and is synchronously triggered by the mode-locked optical fiber laser 1. The acousto-optic modulator 7 is used to pick up a pulse cluster laser with required parameters, and the output of an ultra-short pulse cluster laser with an ultra-high repetition rate and adjustable parameters is realized by adjusting the intracavity gain of the optical fiber ring cavity and picking up synchronous pulses outside the cavity.

[0020] The frequency multiplier utilizes the vernier effect to perform pulse frequency multiplication, which can realize a pulse sequence with arbitrarily adjustable repetition rate and strictly equidistant sub-pulses.

[0021] The mode-locked fiber laser 1 provides a trigger source and an initial base frequency pulse signal for the acousto-optic modulator, and its peak power is within 10 W to prevent pulse splitting and deformation caused by nonlinear effects. Preferably, the mode-locked fiber laser 1 is a mode-locked erbium-doped fiber laser, with a central wavelength of 1550 nm, an average power of 50 mW, a repetition frequency of 12 MHz, a pulse width of 800 fs, and a corresponding peak power of 5 W.

[0022] The input end of the first fiber coupler 2 is connected to the mode-locked fiber laser 1, and the isolation end of the first fiber coupler 1 is connected to the output end of the fiber amplifier 6, the coupling end of the first fiber coupler 1 is connected to the input end of the fiber delay line 3, and the through end of the first fiber coupler 1 is suspended. If the coupling ratio of the first fiber coupler 1 is too small, the power in the fiber ring cavity will be insufficient and effective power amplification cannot be achieved; if the coupling ratio is too large, the loss of the fiber ring cavity will increase and the ring-down time will be reduced. Preferably, the power coupled into the fiber ring cavity by the first fiber coupler 1 is between 10% and 20%. When the power coupled into the fiber circulator by the first fiber coupler 1 is 10%, the coupler splitting ratio used is 90:10.

[0023] The output end of the optical fiber delay line 3 is connected to the dispersion compensating optical fiber 4, which is used to finely adjust the cavity length to achieve dense pulse frequency increase. The delay time directly determines the sub-pulse repetition rate of the pulse cluster. Preferably, this embodiment selects an optical fiber delay line with a delay range of 0-300ps and a delay accuracy within 1ps.

[0024] One end of the dispersion compensating fiber 4 is connected to the output end of the optical fiber delay line 3, and the other end of the dispersion compensating fiber 4 is connected to the input end of the second optical fiber coupler 5. The dispersion value of the dispersion compensating fiber 4 is determined by the total dispersion of the optical fiber ring cavity. As a preferred embodiment, this embodiment ensures that the total dispersion in the optical fiber ring cavity is close to zero. According to the repetition frequency of the locked mode fiber laser 1, it is inferred that if all the optical fibers used are standard single-mode fibers, the total dispersion of the optical fiber ring cavity is about -360ps2 / m. Therefore, a normal dispersion fiber-HI1060 flex with an absolute value close to the standard optical fiber dispersion is selected as the dispersion compensating fiber. Its length is about 8m, which is close to the length of the standard single-mode fiber in the cavity. It can be increased or decreased as appropriate according to actual conditions during the specific implementation process.

[0025] The input end of the second fiber coupler 5 is connected to the dispersion compensation fiber 4, the straight-through end of the second fiber coupler 5 is connected to the seed input end of the fiber amplifier 6, the coupling end of the second fiber coupler 5 is connected to the input end of the acousto-optic modulator 7, and the isolation end of the second fiber coupler 5 is suspended; under the condition of ensuring sufficient output signal strength, the coupled output power of the fiber ring cavity is between 1% and 5%. A smaller coupling output ratio is selected to reduce the loss of the ring cavity. When the coupled output power of the fiber ring cavity is 1%, the coupler splitting ratio used is 99:1.

[0026] The fiber amplifier 6 is composed of a gain fiber, a wavelength division multiplexer, and a pump source. The gain fiber is determined by the initial pulse wavelength provided by the mode-locked fiber laser, and the length of the gain fiber is determined by the total loss in the fiber ring cavity. The pump source is a 980nm butterfly semiconductor laser. Preferably, in order to prevent the ring cavity from oscillating freely, the selected gain fiber length should make the net gain in the cavity lower than the starting threshold.

[0027] According to the ring cavity structure, the cavity loss is estimated to be about 1 dB, so a 20 cm erbium-doped fiber (Liekki, Er80-4 / 125) is selected as the gain fiber. The pump source is a 980 nm butterfly semiconductor laser with a maximum output power of 500 mW.

[0028] The modulation wavelength range of the acousto-optic modulator 7 matches the wavelength of the mode-locked fiber laser 1, and its rise / fall time is less than 15ns, ensuring that the pulse after frequency reduction has a pure spectrum. Preferably, the output end of the acousto-optic modulator 7 is connected to an external measuring device as the output end of the entire ultra-high repetition rate adjustable ultrashort pulse cluster generator, and the external measuring device is an oscilloscope, a spectrum analyzer, etc. The modulation wavelength of the acousto-optic modulator 7 is 1550nm, the modulation frequency is 100MHz, and the rise / fall time is 13ns, ensuring that the pulse after frequency reduction has a pure spectrum.

[0029] Working principle: When the initial base frequency pulse signal is injected into the fiber ring cavity through the input end of the first fiber coupler, the pulse will circulate in the fiber ring cavity for many times, and the pulse signal will be copied once in each cycle. Due to the ring-down effect of the fiber ring cavity, the copied pulse has a certain degree of attenuation, and finally outputs a series of gradually attenuated pulse sequences, and the peak intensity of the pulse sequence has an exponential curve envelope. Since the pulse interval after replication depends on the cavity length of the fiber ring cavity, it has strict uniformity and stability. Assuming that the time interval of the mode-locked pulse is T0, and the time for the pulse to run one circle in the ring is T1, the interval between the pulse after running one circle and the next pulse of the mode-locked fiber laser is T2 = T1 - T0. Since the pulse interval is only related to the cavity length of the mode-locked cavity and the fiber ring cavity, the output pulse spacing is always consistent. Fine adjustment of the fiber delay line can change the pulse interval T2, thereby realizing the output of pulse sequences with different repetition frequencies. Using this vernier effect, ultra-high repetition rate pulse sequences of the order of hundreds of GHz can be achieved. In order to eliminate the decrease in pulse peak value caused by the ring-down effect, a fiber amplifier is used to compensate for the intracavity loss, thereby outputting a smooth pulse sequence. Dispersion compensation fiber is further used to balance the intracavity dispersion to prevent pulse broadening and deformation caused by dispersion accumulation after multiple cycles. The ultra-high repetition rate pulse sequence after fiber ring cavity frequency up-conversion will be further injected into the acousto-optic modulator, which is synchronously triggered by the mode-locked fiber laser to pick up the ultra-high repetition rate ultra-short pulse cluster mode with the required parameters.

[0030] In practical application, such as Figure 1 and Figure 2As shown in the figure, when the 1550 nm initial fundamental frequency pulse signal output by the mode-locked erbium-doped fiber laser is injected into the fiber ring cavity through the input end of the fiber coupler, the pulse will circulate in the cavity for many times, and the pulse signal will be copied once in each cycle. Due to the ring-down effect of the fiber ring cavity, the copied pulse has a certain degree of attenuation, and finally outputs a series of gradually attenuated pulse sequences, and the peak intensity of the pulse sequence has an exponential curve envelope. Since the pulse interval after replication depends on the cavity length of the fiber ring cavity, it has strict uniformity and stability. Since the repetition frequency of the mode-locked pulse is 12 MHz, it is inferred that its pulse interval T0 is 83.33 ns. By adjusting the fiber delay line with an accuracy of 100fs, it is easy to change the time T1 for the pulse to run one circle in the fiber ring cavity to 83.43 ns. Then the interval between the pulse after running one circle and the next pulse of the mode-locked fiber laser is T2= T1 - T0 = 83.43-83.33= 0.1 ns, thereby realizing a pulse sequence with a repetition frequency of 10 GHz. Since the pulse interval is only related to the cavity length of the mode-locked cavity and the fiber ring cavity, the output pulse spacing is always consistent. Further fine-tuning of the fiber delay line can further shorten the pulse interval difference, thereby realizing the output of pulse sequences with different repetition frequencies. Using this cursor effect, ultra-high repetition rate pulse sequences of the order of hundreds of GHz can be achieved in theory. In order to eliminate the pulse peak drop caused by the ring-down effect, an erbium-doped fiber amplifier is used to compensate for the intracavity loss, thereby outputting a smooth pulse sequence. Further, an approximately 8-meter-long HI1060flex optical fiber is used as a dispersion compensation fiber to balance the intracavity dispersion and prevent pulse broadening and deformation caused by the accumulation of dispersion after multiple cycles. After the fiber ring cavity is frequency-increased, the ultra-high repetition rate pulse sequence will be further injected into a synchronously triggered acousto-optic modulator to pick up the ultra-high repetition rate ultra-short pulse cluster mode with the required parameters.

[0031] Beneficial effects: The present invention combines the pulse replication function of the fiber ring cavity with the vernier effect to achieve dense pulse frequency increase; the fiber amplifier is used to compensate for the inherent loss of the ring cavity to solve its inherent ring-down effect. Further, through dispersion compensation, the pulse broadening and distortion caused by the accumulation of dispersion after multiple pulse replications are avoided, thereby achieving the output of a pulse sequence with strictly equidistant sub-pulses and ultra-high repetition rate; finally, through the pulse picking of the synchronous acousto-optic modulator, a pulse cluster laser mode with flexible parameter adjustment can be achieved.

[0032] Compared with the traditional pulse cluster acquisition scheme, the present invention omits the complex intracavity dynamics control, and there is no fluctuation in the sub-pulse spacing caused by pulse collapse and process errors, which breaks through the technical problem of limited repetition frequency. It is a technical solution for ultra-high repetition rate and ultra-short pulse cluster generator with good system stability, simple structure, low cost, and flexible and adjustable parameters, which overcomes the technical difficulties of limited repetition frequency and unequal sub-pulse spacing in traditional schemes. It has broad application prospects in the fields of precision material processing, optical communication systems, scientific research, etc., and has good practicality. The specific description of the present invention in the above embodiments is only used to further illustrate the present invention, and cannot be understood as limiting the scope of protection of the present invention. Technical engineers in this field make some non-essential improvements and adjustments to the present invention based on the content of the above invention, which fall within the scope of protection of the present invention.

Claims

1. An ultra-high repetition rate adjustable ultra-short pulse cluster generator, characterized in that: The invention comprises a mode-locked fiber laser, a first fiber coupler, a fiber delay line, a dispersion-compensating fiber, a second fiber coupler, a fiber amplifier and an acousto-optic modulator. The first fiber coupler, the fiber delay line, the dispersion-compensating fiber, the second fiber coupler and the fiber amplifier are connected end to end in sequence to form a fiber ring cavity, and the ring cavity is used as a frequency multiplier for pulse multiplication. The first fiber coupler is used as an input port of the frequency multiplier, and the second fiber coupler is used as an output port of the frequency multiplier. A baseband pulse signal is input from the first fiber coupler into the fiber ring cavity for frequency multiplication, and a pulse sequence after frequency multiplication is output from the second fiber coupler. The length difference between the fiber ring cavity and the mode-locked cavity in the mode-locked fiber laser is adjusted by the fiber delay line, and the ultra-short pulse sequence with ultra-high repetition rate is realized by using the vernier effect; the dispersion compensation fiber is used to compensate for the dispersion in the cavity and prevent pulse broadening; The fiber amplifier is used to balance the loss in the fiber ring cavity and eliminate the ring-down effect of the fiber ring cavity. The acousto-optic modulator is placed at the output end of the fiber ring cavity and is synchronously triggered by a mode-locked fiber laser. The acousto-optic modulator is used to pick up a pulse cluster laser with required parameters. By adjusting the gain inside the fiber ring cavity and picking up synchronous pulses outside the cavity, the output of an ultra-high repetition rate ultra-short pulse cluster laser with adjustable parameters is achieved.

2. The ultra-high repetition rate adjustable ultra-short pulse cluster generator according to claim 1, characterized in that: The mode-locked fiber laser provides a trigger source and an initial base frequency pulse signal for the acousto-optic modulator, and its peak power is within 10W.

3. The ultra-high repetition rate adjustable ultra-short pulse cluster generator according to claim 2, characterized in that: The input end of the first fiber coupler is connected to the mode-locked fiber laser, and the isolation end of the first fiber coupler is connected to the output end of the fiber amplifier, the coupling end of the first fiber coupler is connected to the input end of the fiber delay line, the through end of the first fiber coupler is suspended, and the power coupled into the fiber ring cavity by the first fiber coupler is between 10% and 20%.

4. The ultra-high repetition rate adjustable ultra-short pulse cluster generator according to claim 3, characterized in that: The output end of the optical fiber delay line is connected to the dispersion compensation optical fiber for finely adjusting the cavity length to achieve dense pulse frequency increase. The delay range of the optical fiber delay line is 0-300ps, and the delay accuracy is within 1ps.

5. The ultra-high repetition rate adjustable ultra-short pulse cluster generator according to claim 4, characterized in that: One end of the dispersion compensating fiber is connected to the output end of the fiber delay line, and the other end of the dispersion compensating fiber is connected to the input end of the second fiber coupler. The dispersion value of the dispersion compensating fiber is determined by the total dispersion of the fiber ring cavity.

6. The ultra-high repetition rate adjustable ultra-short pulse cluster generator according to claim 5, characterized in that: The input end of the second fiber coupler is connected to the dispersion compensation fiber, the through end of the second fiber coupler is connected to the seed input end of the fiber amplifier, the coupling end of the second fiber coupler is connected to the input end of the acousto-optic modulator, and the isolation end of the second fiber coupler is suspended; While ensuring sufficient output signal strength, the coupled output power of the fiber ring cavity is between 1% and 5%.

7. The ultra-high repetition rate adjustable ultra-short pulse cluster generator according to claim 6, characterized in that: The doped ions of the fiber amplifier consist of three parts: a gain fiber, a wavelength division multiplexer, and a pump source. The gain fiber is determined by the initial pulse wavelength provided by a mode-locked fiber laser, the length of the gain fiber is determined by the total loss in the fiber ring cavity, and the pump source is a semiconductor laser.

8. The ultra-high repetition rate adjustable ultra-short pulse cluster generator according to claim 7, characterized in that: The modulation wavelength range of the acousto-optic modulator matches the wavelength of the mode-locked fiber laser, and its rise / fall time is less than 15ns, ensuring that the frequency-reduced pulse has a pure spectrum.

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