Fiber laser pulse height compensation method and system

Abstract

The invention provides an optical fiber laser pulse height compensation method and system, and the method comprises the steps: enabling pump light of a pump source to be coupled with seed light outputted by a seed source module in an amplification module, and achieving the amplification through a gain optical fiber, and obtaining a laser pulse outputted by an optical fiber laser; the pumping source is started, a pre-current is injected into the gain fiber in advance, and the time is maintained for t1; the pumping source is controlled, overshoot current is injected into the gain optical fiber for a certain time, and then main current is continuously output; the duration and the magnitude change of the overshoot current enable the pulse generated after the pre-current is applied to be sunken; and starting the seed source module, wherein the time for starting the seed source module is equal to or later than the time for just injecting the overshoot current. Under the condition that output parameters of a seed source are not changed and low-absorption-coefficient optical fibers are not limited, the problem of pulse front-section sequence sag is compensated only according to a pumping driving mode from gain optical fiber amplification and loss mutual curves.

Description

Technical Field

[0001] The present invention relates to the field of fiber lasers and processing, and particularly to a method and system for compensating the pulse height of a fiber laser. Background Art

[0002] Laser processing utilizes a high-intensity laser beam, which is focused by an optical system to cut, etch, weld, and perform fine microprocessing on materials. Laser processing has significant characteristics such as high efficiency, high speed, small deformation, high precision, and low energy consumption. Laser processing is gradually developing towards refinement and intelligence. New production requirements and application scenarios are constantly emerging, and the technical level and optical indicators of laser processing equipment will also be further improved.

[0003] Currently, in the high-end laser demand market, there is little research on the absorption and gain of pulses affected by fiber characteristics, and effective control of optical pulse amplification cannot be achieved. As a result, the laser has problems such as amplified output pulse jitter, large differences in pulse height, and poor optical pulse processing effects. Most existing methods use the method of selecting low-absorption and low-gain fibers, resulting in a simultaneous decrease in pump absorption and amplification efficiency. In addition, there are also some methods of introducing an ASE light source to control background noise, but the actual operability is relatively small.

[0004] As Figure 1 shown, a fiber laser generally includes a seed source module 1 and a multi-stage amplification module. The seed source module 1 includes a semiconductor LD seed source and a seed light output editing circuit. The semiconductor LD seed source outputs seed light after passing through the seed light output editing circuit. The seed light sequentially passes through each stage of the amplification module to complete power amplification. Among them, the seed light output editing circuit can arbitrarily control the shape width, output frequency, and output time of the pulses output by the semiconductor LD seed source.

[0005] The amplification module includes at least two stages of amplification modules, and an isolator is used to block the return light between each stage of the amplification module to protect the optical path. Figure 1 The optical path structure diagram of an optical path including two stages of amplification modules is listed in , and its optical path structure is a typical MOPA amplification method. The seed light output by the seed source module 1 sequentially passes through the pre-amplification module 2 and the main amplification module 3 to complete power amplification. The pre-amplification module 2 includes a first control module 2-1, a pre-amplification stage pump source 2-2, a first coupler 2-3, a first gain fiber 2-4, and a first optical isolator 2-5. The current output by the pre-amplification stage pump source 2-2 is controlled by the first control module 2-1. The main amplification module 3 includes a second control module 3-1, a main amplification stage pump source 3-2, a second coupler 3-3, a second gain fiber 3-4, and a second optical isolator 3-5. The current output by the main amplification stage pump source 3-2 is controlled by the second control module 3-1. Along the direction of pulse light transmission, a cladding light stripper is arranged behind the second optical isolator 3-5 to remove the remaining pulse light.

[0006] In the prior art, the seed source module 1 and the first control module 2-1 are started simultaneously, so that the seed light output by the seed source module 1 and the pump light output by the pre-amplification stage pump source 5 enter the first coupler 6 together, and then enter the first gain fiber 7 to form population inversion, completing the first-stage power amplification of the pulsed light. Then the pulsed light enters the second coupler 11 through the first optical isolator 8. At the same time, the second control module 9 is started, so that the pulsed light processed by the pre-amplification module 2 and the pump light output by the main amplification stage pump source 10 enter the second coupler 11 simultaneously, and then enter the second gain fiber 12 to complete the second-stage power amplification, and the backward light is blocked by the second isolator 13. The remaining pulsed light is removed by the cladding light stripper arranged behind the second isolator 13.

[0007] Among them, the seed light output by the seed source module 1 only changes in efficiency after passing through components such as passive transmission fibers and spatial optical devices, without affecting the pulse consistency. That is to say, the pulse height of the seed light output by the seed source module 1 is consistent before entering the amplification module. However, due to the low absorption and saturation characteristics of the gain fiber in the 1-μm wavelength region of the laser, the pumping of the gain fiber by the pump source cannot be instantaneously converted into optical pulse amplification, resulting in strong absorption of the initial pulsed light at the gain fiber and the absorption intensity decreasing exponentially, that is, the leading pulse of the pulsed light output after passing through the amplification module shows an absorption curve consumption as Figure 2 shown.

[0008] Since the absorption conversion time at the moment of light output from the pump source is on the order of several microseconds, the pump energy cannot be fully absorbed and amplified by the gain fiber. Therefore, the first pulse needs to absorb part of the energy injected during the pre-injection stage to complete the compensation. Specifically, before starting the seed source module 1, the first control module 2-1 is started in advance, so that the pre-amplification stage pump source 2-2 injects a pre-current into the first gain fiber 2-4 in advance for several milliseconds, that is, no seed light is input into the first gain fiber 2-4 during the injection of the pre-current. At this time, the seed source module 1 is not started, and part of the injected pre-current is converted into spontaneous emission loss, and the other part of the pump energy reaches the upper energy level particle equilibrium state during the pre-injection time. Then, the main current I1 is input through the pump source, and at the same time, the seed source module 1 is started, that is, the application of the main current I1 is synchronized with the output light time of the seed source module 1. Among them, the rising duration of the pump source (that is, the time for the pump source to rise from the pre-current on to the main current) is usually 1-10 microseconds, and the turn-off time (that is, the time from the main current off to 0) is 0.5-5 microseconds. As Figure 3 shown, this pre-current compensation method raises a section of the first pulse from complete absorption to a certain pulse distribution value, but there is still a problem of pulse depression within several hundred microseconds. Usually, the pulse depression time t2 is in the sub-millisecond level, and the depression depth can reach 20%-50%.

[0009] Currently, the first pulse compensation often adopts the method of injecting a pre-current as described above. At specific parameters, the maximum pre-current still cannot effectively increase the height of the first pulse. The pre-current time t1 reaches a steady-state balance in milliseconds, that is, continuing to increase t1 will not increase the height of the first pulse in the optical fiber. In addition, an excessive pre-current value will cause the first pulse to seriously exceed the limit. If a single pulse exceeds the threshold, it will damage the optical fiber (i.e., cause strong spontaneous emission to burn out the optical fiber). Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a method and system for compensating the height of an optical fiber laser pulse, which can optimize the flatness of the laser pulse in the initial period of a pulse laser.

[0011] The technical solution adopted by the present invention to solve the above technical problem is: A method for compensating the height of an optical fiber laser pulse, which is used for an optical fiber laser. The optical fiber laser includes a seed source module and an amplification module. In the amplification module, the pump light of the pump source is coupled with the seed light output by the seed source module, and then amplified through a gain optical fiber to obtain the laser pulse output by the optical fiber laser. It is characterized in that it includes the following steps:

[0012] S1. Start the pump source, inject a pre-current into the gain optical fiber in advance, and maintain it for a time t1.

[0013] S2. Control the pump source to first inject an overshoot current into the gain optical fiber for a certain period of time, and then continuously output the main current; the duration and magnitude change of the overshoot current make up for the pulse depression generated after applying the pre-current.

[0014] S3. Start the seed source module, and the start time of the seed source module is equal to or later than the time when the overshoot current is just injected.

[0015] The pulse depression is obtained by the following method: Start the pump source, inject a pre-current into the gain optical fiber in advance, and maintain it for a time t1; then control the pump source to inject the main current into the gain optical fiber, and at the same time start the seed source module to obtain the laser pulse curve output by the optical fiber laser. The laser pulses that do not reach the predetermined height form a pulse depression.

[0016] According to the above solution, the amplification module has at least two stages, and each stage of the amplification module includes a pump source, a coupler, and a gain optical fiber; the laser pulse output by the optical fiber laser is the comprehensive superposition of the compensation of each stage of the amplification module;

[0017] Each stage of the amplification module simultaneously completes steps S1 and S2. The superposition of the duration and magnitude change of the overshoot current generated by each stage of the amplification module makes up for the pulse depression after the comprehensive superposition;

[0018] The time to start the seed source module is equal to or later than the time when each stage of the amplification module has just injected an overshoot current;

[0019] The pulse depression after comprehensive superposition is obtained as follows: Start each stage of the amplification module simultaneously, and respectively inject a pre-current into each stage of the gain fiber in advance for a maintenance time t1; Control each stage of the pump source to inject the main current into the corresponding gain fiber, and start the seed source module simultaneously to obtain the laser pulse curve after comprehensive superposition. The laser pulses that do not reach the predetermined height form pulse depressions.

[0020] According to the above scheme, the amplification module further includes a control module for controlling the output power of the pump source, thereby realizing the adjustment of the current magnitude injected into the gain fiber.

[0021] According to the above scheme, the pump source in each stage of the amplification module determines the range of the overshoot current according to the pump main current and the amplification factor.

[0022] According to the above scheme, the pre-current < 2A; the maintenance time t1 of the pre-current is within 10 milliseconds.

[0023] According to the above scheme, the magnitude of the main current is 2 - 20A.

[0024] According to the above scheme, the overshoot current is 1.3 - 3 times the main current.

[0025] According to the above scheme, the relationship between the magnitude of the overshoot current and the pulse depression is: the deeper the pulse depression, the larger the overshoot current; the shallower the pulse depression, the closer the overshoot current is to the main current;

[0026] The duration of the overshoot current is equal to the duration of the pulse depression.

[0027] According to the above scheme, the duration and magnitude change of the overshoot current are determined according to experimental calibration and then used as preset values.

[0028] An optical fiber laser pulse height compensation system includes a control unit, which is used to implement the above-mentioned optical fiber laser pulse height compensation method when called.

[0029] The beneficial effects of the present invention are as follows: Without changing the output parameters of the seed source and without being limited to low-absorption coefficient optical fibers, before starting the seed source module, in the amplification module, according to the pump drive mode, starting from the curve of gain fiber amplification and loss, the problem of the depression of the front sequence of the pulse is compensated; what is obtained after starting the seed source module is a flat laser pulse. The present invention can adapt to the dip depth compensation under all frequency and pulse width parameters, and the same compensation curve can adapt to a wide frequency range and the similar curves of each stage of amplification current, greatly simplifying the circuit control complexity, optimizing the output pulse consistency of the pulsed laser, being able to completely make up for the problem of the starting pulse intensity common in laser processing, and having a great promoting effect on the expansion of laser technology to precision machining applications. Description of the Drawings

[0030] Figure 1 It is a schematic diagram of the optical path structure of a fiber laser in the prior art.

[0031] Figure 2 It is a pulse absorption curve diagram in the prior art.

[0032] Figure 3 It is an effect diagram of the first pulse with pre-current compensation.

[0033] Figure 4 It is an effect diagram of current editing compensation.

[0034] In the figure:

[0035] 1 - Seed source module;

[0036] 2 - Pre-amplification module, 2 - 1 - First control module, 2 - 2 - Pre-amplification stage pump source, 2 - 3 - First coupler, 2 - 4 - First gain fiber, 2 - 5 - First optical isolator;

[0037] 3 - Main amplification module, 3 - 1 - Second control module, 3 - 2 - Main amplification stage pump source, 3 - 3 - Second coupler, 3 - 4 - Second gain fiber, 3 - 5 - Second optical isolator. Detailed Embodiment

[0038] The present invention will be further described below in conjunction with specific examples and drawings.

[0039] A fiber laser generally includes a seed source module and multiple stages of amplification modules. The seed source module outputs seed light, and the seed light sequentially passes through each stage of amplification module to complete power amplification.

[0040] In this embodiment, taking two-stage amplification as an example, the present invention is further explained.

[0041] Figure 1The optical path structure diagram of a fiber laser including a two-stage amplification module is listed. Its optical path structure is a typical MOPA amplification method. The seed light output by the seed source module 1 is sequentially amplified in power through the pre-amplification module 2 and the main amplification module 3. The pre-amplification module 2 includes a first control module 2-1, a pre-amplification stage pump source 2-2, a first coupler 2-3, a first gain fiber 2-4, and a first optical isolator 2-5. The magnitude of the current output by the pre-amplification stage pump source 2-2 is controlled by the first control module 2-1. The main amplification module 3 includes a second control module 3-1, a main amplification stage pump source 2-2, a second coupler 3-3, a second gain fiber 3-4, and a second optical isolator 3-5. The magnitude of the current output by the main amplification stage pump source 2-2 is controlled by the second control module 3-1. Along the direction of pulsed light propagation, a cladding light stripper is arranged behind the second optical isolator 3-5 to remove the remaining pulsed light. The laser pulse output by the fiber laser is the comprehensive superposition compensated by the two-stage amplification module.

[0042] The present invention provides a method for compensating the height of a fiber laser pulse, which is used for the above-mentioned fiber laser, and specifically includes the following steps:

[0043] S1. Start the first control module 2-1 to control the pre-amplification stage pump source 2-2, and inject a pre-current (generally less than 2 A, preferably less than 1 A) into the first gain fiber 2-4 in advance, and maintain it for a time t1. t1 is a preset value, usually within 10 milliseconds. The first control module 2-1 is electrically connected to the pre-amplification stage pump source 2-2. The pre-amplification stage pump source 2-2 and the seed source module 1 are respectively connected to the input end of the first coupler 2-3 through an optical path (fiber). The output end of the first coupler 2-3 is connected to the first gain fiber 2-4, and then outputs through the first optical isolator 2-5.

[0044] At the same time, start the second control module 3-1 to control the main amplification stage pump source 2-2, and inject a pre-current (generally less than 2 A, preferably less than 1 A) into the second gain fiber 3-4 in advance. The maintenance time is the same as the maintenance time of the pre-current of the pre-amplification module. The second control module 3-1 is electrically connected to the main amplification stage pump source 2-2. The main amplification stage pump source 2-2 and the output end of the first optical isolator 2-5 are respectively connected to the input end of the second coupler 3-3 through an optical path (fiber). The output end of the second coupler 3-3 is connected to the second gain fiber 3-4, and then outputs through the second optical isolator 3-5.

[0045] S2, control the pre-amplification stage pump source 2-2 through the first control module 2-1, inject an overshoot current into the first gain fiber 2-4 for a certain period of time, and then continuously output the main current; at the same time, control the main amplifier stage pump source 3-2 through the second control module 3-1, inject an overshoot current into the second gain fiber 3-4 for a certain period of time, and then continuously output the main current. At this time, the current in the first gain fiber 2-4 and the second gain fiber 3-4 is rapidly pulled up from the pre-current to the main current size and continues to rise to the overshoot state, and after maintaining the overshoot for a certain period of time, the main current size tends to be stable.

[0046] The superposition of the duration and magnitude of the overshoot currents of the pre-amplification module 2 and the main amplification module 3 makes up for the pulse depression after the comprehensive superposition.

[0047] The pulse depression after comprehensive superposition is obtained by the following method: the pre-amplification module and the main amplification module are started simultaneously, and a pre-current is respectively injected into each level of gain fiber (i.e., the first gain fiber 2-4 and the second gain fiber 3-4) in advance, and maintained for time t1; each level of pump source (i.e., the pre-amplification stage pump source 2-2 and the main amplification stage pump source 3-2) is controlled to inject the main current into the corresponding gain fiber (i.e., the first gain fiber 2-4 and the second gain fiber 3-4), and the seed source module 1 is started at the same time, and the laser pulse curve after comprehensive superposition is obtained, and the laser pulse that does not reach the predetermined height forms a pulse depression, such as Figure 3 As shown, the duration of the pulse depression is t2. S4, the time of starting the seed source module is equal to or later than the time when each stage of the amplification module just generates the overshoot current, so as to ensure that the laser pulse obtained at this time is flat, as shown in FIG. Figure 4 As shown. Since the laser pulses of the same parameter sequence output by the seed source module 1 pass through the pre-amplifier module 2 and the main amplifier module 3 in sequence, during this process, the front section of the pulse sequence is absorbed and attenuated by the gain fiber, and the pre-amplifier module 2 needs to perform the first pulse alignment compensation for the pulse sequence, or form the pre-amplifier module 2 output overshoot compensation, and the main amplifier module 3 is attenuated.

[0048] The principle of the present invention is to instantly increase the photocurrent, edit the current overshoot curve to completely compensate for the pulse sag, and the pump pre-current value and the overshoot current curve can be adjusted according to specific circumstances.

[0049] The current editing of the pre-amplifier module 2 and the main amplifier module 3 have different capabilities for increasing the pulse height at the depression. Usually, the main amplifier module 3 can only perform compensation after the pre-amplifier module 2 has been edited and compensated. In addition, the current output by the main amplifier module 3 has a greater impact on the depression, and adjusting the pre-amplifier module 2 can more accurately complete the compensation.

[0050] Similarly, the amplification module can also be a multi-stage amplification module such as a three-stage or four-stage one. The amplification factor of the multi-stage amplification module is determined according to the peak power and spectrum of light. By appropriately dividing the amplification power of each stage of the amplification module, the normal output of the optical fiber optical path amplification can be ensured, and at the same time, the pump energy of each stage can be reasonably distributed. Multi-stage synchronous compensation can achieve a higher pulse flatness under different parameter conditions. For the multi-stage amplification module, it is amplified step by step from low to high. For example, the pre-amplification module 2 amplifies from 1 mW to 1 W, and the main amplification module 3 amplifies from 1 W to 100 W. By setting the multi-stage amplification module, the finally output power can reach the desired power. There is an optical conversion efficiency relationship between the pump energy and the output power of the amplification module. Usually, the conversion efficiency is 60-80%. The greater the amplification power, the greater the required pump energy.

[0051] Among them, the pump source in each stage of the amplification module selects an appropriate overshoot current range according to the pump main current and the amplification factor. If the overshoot current is too large, it will cause damage to the optical fiber. The specific actual overshoot current value is determined according to the compensation measurement effect. Usually, the overshoot current is 30%-300% larger than the main current. The actual current compensation curve in each stage of the amplification module is determined according to the dip depth and dip time. Specifically, as Figure 4 shown, after inputting the pre-current, the current output by the pre-amplification stage pump source 2-3 is quickly pulled up to the overshoot current I2 through the first control module 2-2 to improve the flatness at the dip outside the pre-current control; since the current rise time (i.e., the time to apply the overshoot current, i.e., t4) has little influence on the first pulse, the accuracy of the pulse dip compensation can correspond to t2. Generally, the dip can be accurately compensated in the microsecond order, that is, the current rise time t4 is the same as the pulse dip time t2, that is, t4 = t2.

[0052] In this embodiment, the overshoot current I2 is 30%-300% larger than the main current I1, that is, I2 = 1.3 - 3I1, and the main current I2 = 2 - 20 A.

[0053] From Figure 4 it can be seen that in this embodiment, the front part of the dip responds less to the current rise, so a larger current compensation is required, that is, a larger overshoot current I2 is required. The response of the rear part of the dip to the current rise gradually increases, that is, the dip compensation effect becomes gradually obvious, and the required overshoot current I2 gradually decreases until I2 = I1. That is, the overshoot current value I2 applied corresponds to the deepest part of the pulse dip. The deeper the dip, the larger the overshoot current I2, and the shallower the dip, the closer the overshoot current I2 is to the main current I1.

[0054] In this embodiment, after applying the overshoot current I2 for a certain time, the seed source module 1 is started again, that is, as Figure 4As shown, after applying a pre-current for time t1, the seed source module 1 is turned on after an additional time t3. By delaying the start of the seed source module 1 by time t3, the first pulse of the main current I1 during the excitation period is amplified, thus avoiding damage to the gain fiber caused by the long-term injection of a large pre-current. When the depression is too large or the overshoot current I2 cannot meet the compensation requirements under certain parameters, compensation can be achieved by controlling t3, but t3 cannot exceed 1 millisecond, otherwise there is a risk of damaging the fiber.

[0055] The depth of the depression mainly depends on the frequency and pulse width parameters. Generally, the higher the frequency and the wider the pulse width, the greater the depth of the depression (the deeper the depression, the longer the depression time). The same compensation curve can be applied to a certain parameter range, and the compensation curve can be linearly transformed under different powers. A reasonable current curve setting can fully compensate for the pulse differences under all parameters. Therefore, for certain parameters, after experimentation, the overshoot current curve can be obtained and calibrated as a preset value, and the pump source can be directly controlled according to this curve. For example, first, according to the method of obtaining the pulse depression, use an oscilloscope to measure the pulse height to obtain the specific duration t2 of the pulse depression and the pulse height curve; then, according to the principle that "the deeper the pulse depression, the larger the overshoot current; the shallower the pulse depression, the closer the overshoot current is to the main current", debug the pump sources of each amplification module and measure the debugging results with an oscilloscope; according to the results, if there is still a depression, increase the overshoot current, and if the pulse is too high, decrease the overshoot current until it reaches the preset error range. Then record the duration and curve of the overshoot current at this time as the preset value, that is, the calibration is completed.

[0056] The same current curve of the present invention can be applied to the depression compensation under certain pulse width, frequency, and power conditions during the development process, and has strong adaptability for laser development.

[0057] The seed source module 1 can be a nanosecond, picosecond, or femtosecond seed source.

[0058] The gain fiber can be polarization-maintaining fiber, non-polarization-maintaining fiber, or photonic crystal fiber. The types of gain fibers include 10 / 125, 20 / 125, 20 / 400, 30 / 250, 40 / 250, 50 / 400, etc.; or the gain fiber is a double-clad fiber such as 10 / 130μm, 30 / 250μm, 100 / 400μm, etc., which is sufficiently adaptable for various single-mode small-core and multi-mode large-core applications.

[0059] The center wavelength of the pump source is 915nm or 976nm, etc.

[0060] The laser center wavelength of the gain fiber is 1030nm, 1064nm, 1550nm, etc.

[0061] The optical coupler is a 2+1, 6+1, or 18+1 coupler.

[0062] The pumping method of each stage of the amplification module can be forward pumping, backward pumping or bidirectional pumping.

[0063] This embodiment also provides a fiber laser pulse height compensation system, including a control unit, which is used to implement the fiber laser pulse height compensation method when called. Specifically, the control unit of this system is connected to the control modules of each stage of the amplification module and controls the switch of the seed source module; or directly preset the calibrated overshoot current curve in the control modules of each stage of the amplification module and set the delayed start time of the seed source module.

[0064] Without changing the output parameters of the seed source and without being limited to low-absorption coefficient fibers, the present invention compensates for the depression problem of the front-segment sequence of pulses starting from the mutual curve of gain fiber amplification and loss only based on the pump drive mode. It can adapt to the dip depth compensation under all frequencies and pulse width parameters, and the same compensation curve can adapt to a wide frequency range and similar curves of each stage of amplification current, greatly simplifying the circuit control complexity, optimizing the output pulse consistency of the pulsed laser, and being able to completely make up for the common starting pulse intensity problem in laser processing, which has a great promoting effect on the expansion of laser technology to precision processing applications.

[0065] It should be understood that those of ordinary skill in the art can make improvements or transformations according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for compensating the pulse height of a fiber laser, which is used for a fiber laser. The fiber laser includes a seed source module and an amplification module. In the amplification module, the pump light of a pump source is coupled with the seed light output by the seed source module, and then amplified through a gain fiber to obtain the laser pulse output by the fiber laser. It is characterized in that: It includes the following steps: S1. Start the pump source, inject a pre-current into the gain fiber in advance, and maintain it for a time t1; S2. Control the pump source to first inject an overshoot current into the gain fiber for a certain period of time, and then continuously output the main current; the duration and magnitude change of the overshoot current make up for the pulse depression generated after applying the pre-current; S3. Start the seed source module, and the time to start the seed source module is equal to or later than the time when the overshoot current is just injected; The pulse depression is obtained in the following way: Start the pump source, inject a pre-current into the gain fiber in advance, and maintain it for a time t1; then control the pump source to inject the main current into the gain fiber, and at the same time start the seed source module to obtain the laser pulse curve output by the fiber laser, and the laser pulses that do not reach the predetermined height form the pulse depression.

2. The fiber laser pulse height compensation method according to claim 1, characterized in that: The amplification module has at least two stages, and each stage of the amplification module includes a pump source, a coupler and a gain fiber; the laser pulses output by the fiber laser are the comprehensive superposition compensated by each stage of the amplification module; Each stage of the amplification module simultaneously completes steps S1 and S2, and the superposition of the duration and magnitude change of the overshoot current generated by each stage of the amplification module makes up for the pulse depression after the comprehensive superposition; The time to start the seed source module is equal to or later than the time when each stage of the amplification module just injects the overshoot current; The pulse depression after the comprehensive superposition is obtained in the following way: Start each stage of the amplification module simultaneously, inject a pre-current into each stage of the gain fiber in advance, and maintain it for a time t1; control each stage of the pump source to inject the main current into the corresponding gain fiber, and at the same time start the seed source module to obtain the laser pulse curve after the comprehensive superposition, and the laser pulses that do not reach the predetermined height form the pulse depression.

3. The method for compensating the height of an optical fiber laser pulse according to claim 1 or 2, characterized in that: The amplification module further includes a control module for controlling the output power of the pump source, so as to realize the adjustment of the magnitude of the current injected into the gain fiber.

4. The method for compensating the height of an optical fiber laser pulse according to claim 2, characterized in that: The pump source in each stage of the amplification module determines the range of the overshoot current according to the pump main current and the amplification factor.

5. The fiber laser pulse height compensation method according to claim 1 or 2 or 4, characterized in that: The pre-current < 2A; the maintenance time t1 of the pre-current is within 10 milliseconds.

6. The method for compensating the pulse height of a fiber laser according to claim 1 or 2 or 4, characterized in that: The magnitude of the main current is 2 - 20A.

7. The method for compensating the height of an optical fiber laser pulse according to claim 1 or 2 or 4, characterized in that: The overshoot current is 1.3 - 3 times the main current.

8. The method for compensating the pulse height of a fiber laser according to claim 1 or 2, characterized in that: The relationship between the magnitude of the overshoot current and the pulse depression is: the deeper the pulse depression, the larger the overshoot current; the shallower the pulse depression, the closer the overshoot current is to the main current; The duration of the overshoot current is equal to the duration of the pulse depression.

9. The method for compensating the pulse height of a fiber laser according to claim 1 or 2 or 4, characterized in that: The duration and magnitude change of the overshoot current are determined according to experimental calibration and then used as preset values.

10. A fiber laser pulse height compensation system, characterized in that: It includes a control unit, which is used to implement the fiber laser pulse height compensation method described in any one of claims 1 to 9 when called.

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