2 [mu] m nanosecond pulse fiber laser and time domain waveform adjusting method thereof

Abstract

The invention discloses a 2 [mu] m nanosecond pulse fiber laser and a time domain waveform adjustment method thereof. The laser comprises a seed source module and an amplification module connected with the seed source module. The seed source module comprises a first high-reflectivity fiber bragg grating, an acoustic optical modulator, a first beam combiner, a first thulium-doped fiber, a 2 * 2 coupler and a second high-reflectivity fiber bragg grating which are connected in sequence, as well as a driving source connected with the acoustic optical modulator and a first pumping source connected with the first beam combiner; the amplification module comprises an online isolator, a second beam combiner, a second thulium-doped optical fiber and an output jumper which are connected in sequence, and a second pumping source connected with the second beam combiner; the rising edge time and the starting time of the acousto-optic modulator are subjected to parameter setting through a human-computer interface of the driving source; the wavelengths of lasers output by the first pumping source and the second pumping source are both 793 nanometers. According to the invention, the multi-peak phenomenon of the Q-switched pulse laser of the 2um waveband can be conveniently and effectively eliminated, the performance of the laser is improved, and the application requirements of low cost and mass production are met.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber link detection, and in particular to a time domain waveform adjustment method for a 2um nanosecond pulse optical fiber laser. Background Art

[0002] A Q-switched pulsed laser is a device that can produce high peak power, short pulse width lasers. By adjusting the "Q factor" (quality factor) of the laser cavity, the laser can output laser light in the form of pulses. The Q-switching process involves periodically changing the loss or gain of the laser cavity to achieve high energy density laser pulses. The 2um wavelength usually refers to the mid-infrared band, and this wavelength of light is very useful in some high-precision applications, such as in lidar, spectral analysis, and some medical equipment.

[0003] In the prior art, 2um nanosecond pulse fiber lasers are generally implemented by gain modulation or electrically modulated seeds. Gain modulation uses 1550nm laser pulse pumping, converts 1550nm laser into 2um seed light through the absorption of thulium-doped fiber, and then amplifies it. However, the 1550nm laser pulse pump itself is a pulse fiber laser. Compared with the traditional semiconductor laser pump source, the cost of 1550nm laser pulse pumping is higher, the optical path is complex, and it is not suitable for mass production. In addition, due to the low pump energy per cycle, the final output 2um laser pulse width is high, resulting in low peak power, which affects the efficiency of use. Electrical modulation uses electrically modulated 2um semiconductor laser seeds. The output power of this seed is generally in the milliwatt level, and it needs to be amplified in multiple stages to obtain the desired power. This method is costly and can only be used at high frequencies (greater than 100kHz), resulting in low pulse energy and low peak power. At low frequencies (less than 100kHz), due to the weak seed power, the spontaneous radiation in its optical path system is difficult to suppress, resulting in the burning of the optical path.

[0004] Using an acousto-optic modulator (AOM) to generate a Q-switched pulse laser is a common solution for 1um industrial lasers. However, when this solution is used for a 2um Q-switched pulse laser, the output pulse waveform has a distortion problem and may have a multi-peak phenomenon. The multi-peak phenomenon will seriously affect the efficiency of medical treatments such as lithotripsy and soft tissue cutting, and will also affect the precision and efficiency during precision machining. In addition, the current waveform adjustment can only be adjusted slowly by changing the cavity length, rising edge, and switching time through experiments, which takes a long time and has low adjustment efficiency. For example, the Chinese patent "A control method for eliminating the uneven output pulse of a Q-switched pulse fiber laser" with publication number CN106785837A requires continuous changes in the cavity length, rising edge, and switching time to eliminate the multi-peak phenomenon of a 2um Q-switched pulse laser. The adjustment method is complicated and has poor practicality, and it is impossible to achieve low cost and mass production requirements.

[0005] Therefore, it is necessary to propose a 2um nanosecond pulse fiber laser and its time domain waveform adjustment method to eliminate the multi-peak phenomenon of the output pulse, reduce the possible distortion of the waveform, and improve the performance of the 2um Q-switched pulse fiber laser. At the same time, it can simplify the waveform adjustment steps to meet the application requirements of low cost and mass production. Summary of the invention

[0006] In view of this, the present invention provides a 2um nanosecond pulse fiber laser and a time domain waveform adjustment method thereof, so as to solve the technical problems that when the existing acousto-optic modulator is used in a 2um Q-switched pulse laser, the output pulse waveform may have a multi-peak phenomenon, and the method for eliminating the multi-peak phenomenon is complicated, and it is impossible to achieve low-cost mass production and rapid adjustment of the laser.

[0007] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a 2um nanosecond pulse fiber laser, the pulse fiber laser comprising a seed source module and an amplification module connected to the seed source module;

[0009] The seed source module includes a first high-reflectivity fiber Bragg grating, an acousto-optic modulator, a first beam combiner, a first thulium-doped fiber, a 2*2 coupler, and a second high-reflectivity fiber Bragg grating connected in sequence, and also includes a driving source connected to the acousto-optic modulator and a first pump source connected to the first beam combiner;

[0010] The amplification module includes an online isolator, a second beam combiner, a second thulium-doped optical fiber and an output jumper connected in sequence, and a second pump source connected to the second beam combiner;

[0011] The rising edge time and the opening time of the acousto-optic modulator are parameterized through the human-machine interface of the driving source; and the laser wavelengths output by the first pump source and the second pump source are both 793 nm.

[0012] Furthermore, the cavity length of the laser is 23-25m.

[0013] Furthermore, the online isolator is a double-stage online isolator with bandpass filtering.

[0014] Furthermore, the central wavelength of the online isolator is 1940nm and the average power is 10W.

[0015] Furthermore, the optical parameters of the first beam combiner are: 10 / 130 input and 10 / 130 output.

[0016] Furthermore, the optical parameters of the second beam combiner are: 10 / 130 input and 25 / 250 output.

[0017] Furthermore, the power distribution ratio of the 2*2 coupler is 75 / 25.

[0018] On the other hand, the present invention also provides a 2um nanosecond pulse fiber laser time domain waveform adjustment method, the method is applied to the 2um nanosecond pulse fiber laser described in any of the above technical solutions; the time domain waveform adjustment method comprises:

[0019] Determining the driving rising edge time and the opening time of the acousto-optic modulator based on the cavity length of the laser and the frequency of the laser to be output;

[0020] Setting parameters of the acousto-optic modulator according to the rising edge time and the opening time;

[0021] The first pump source and the second pump source are turned on to output Q-switched pulse lasers that eliminate the multi-peak phenomenon.

[0022] Furthermore, the calculation method of the rising edge time s is:

[0023]

[0024] The calculation method of the opening time T is:

[0025]

[0026] Where n is the refractive index of the optical fiber, c is the speed of light, l is the cavity length, f is the laser frequency, and A and B are both constants.

[0027] The present invention provides a 2um nanosecond pulse fiber laser and a time domain waveform adjustment method thereof. First, the laser of the present invention uses a high reflectivity fiber grating and a thulium-doped fiber to ensure the stability and efficient amplification of the laser mode. Secondly, the cooperation of an acousto-optic modulator (AOM) and a driving source allows precise control of the rising edge time and the opening time, thereby improving the quality of the pulse waveform and reducing distortion and multi-peak phenomena. By optimizing the wavelength matching (793 nanometers) of the pump source and designing an efficient fiber combiner and isolator, after setting the rising edge time and the opening time of the acousto-optic modulator, the first pump source and the second pump source can be turned on, thereby outputting a 2um band Q-switched pulse laser that eliminates the multi-peak phenomenon, which can better adapt to the needs of the 2um band, improve the peak power and reduce the cost. The adjustment method is simple and fast, meets the use requirements of low cost and mass production, and realizes large-scale batch production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a light path structure diagram of a 2um nanosecond pulse fiber laser provided by the present invention;

[0029] Figure 2 A schematic diagram of an output waveform when the current provided by the present invention is 3A;

[0030] Figure 3 A schematic diagram of an output waveform when the current provided by the present invention is 4A;

[0031] Figure 4 A schematic diagram of an output waveform when the current provided by the present invention is 5A;

[0032] In the figure, 1-the first high reflectivity fiber Bragg grating, 2-acousto-optic modulator, 3-the first combiner, 4-the first thulium-doped fiber, 5-2*2 coupler, 6-the second high reflectivity fiber Bragg grating, 7-driving source, 8-the first pump source, 9-online isolator, 10-the second combiner, 11-the second thulium-doped fiber, 12-output jumper, 13-the second pump source. DETAILED DESCRIPTION

[0033] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0034] Before introducing the embodiments of the present invention, the concept of the present invention is briefly introduced.

[0035] The 2um wavelength usually refers to the mid-infrared band. Light of this wavelength is very useful in some high-precision applications, such as in lidar, spectral analysis, and some medical equipment. Using acousto-optic modulation (AOM) to generate Q-switched pulse lasers is a common solution for 1um industrial lasers, but this solution has output pulse waveform distortion and multi-peak phenomenon when used for 2um Q-switched pulse lasers. The adjustment methods mainly include: adjusting the pump power, repetition frequency, AOM drive signal duty cycle, etc.

[0036] Increasing the pump power, reducing the repetition frequency and reducing the duty cycle of the AOM drive signal can reduce the number of pulse multi-peaks. However, when the pump power increases to a certain value, the pulse output waveform will become chaotic and the output will be irregular pulses.

[0037] Reducing the repetition frequency will increase the single pulse energy of the system, thereby increasing the peak power of the pulse, and will also cause the pulse output waveform to become chaotic, outputting irregular pulses;

[0038] Reducing the duty cycle of the AOM drive signal increases the accumulation of the inverted particle population, while reducing the AOM opening time. When the time is reduced to a certain value, the output pulse may not be fully released, resulting in excessive accumulation of the upper energy level particles, causing amplified spontaneous radiation.

[0039] Changing the rising edge time of the driver can improve the waveform of the output pulse, but changing the frequency and current will still cause changes in the waveform.

[0040] The 2um nanosecond pulse fiber laser and the adjustment method thereof proposed in the present invention improve the structure of the laser, coordinate the pump power, repetition frequency, AOM drive signal duty cycle and driver rising edge and other parameters based on the optical path structure, comprehensively consider the influence of various factors on the pulse multi-peak phenomenon, can quickly adjust the parameters of the laser, and optimize the pulse laser output waveform in the 2um band.

[0041] See also Figure 1 The present invention provides a 2um nanosecond pulse fiber laser. Figure 1 The optical path structure diagram of the 2um nanosecond pulse fiber laser includes a seed source module and an amplification module connected to the seed source module;

[0042] The seed source module includes a first high reflectivity fiber grating 1, an acousto-optic modulator 2, a first beam combiner 3, a first thulium-doped fiber 4, a 2*2 coupler 5, and a second high reflectivity fiber grating 6 connected in sequence, and also includes a driving source 7 connected to the acousto-optic modulator 2, and a first pump source 8 connected to the first beam combiner 3;

[0043] The amplification module includes an online isolator 9, a second beam combiner 10, a second thulium-doped optical fiber 11 and an output jumper 12 connected in sequence, and a second pump source 13 connected to the second beam combiner 10;

[0044] The rising edge time and the opening time of the acousto-optic modulator 2 are parameterized through the human-machine interface of the driving source 7; the laser wavelengths output by the first pump source 8 and the second pump source 13 are both 793 nm.

[0045] In the above scheme, the first high reflectivity fiber grating 1 is used as a reflector to form the cavity of the fiber laser. The time characteristics of the laser pulse are modulated by the acousto-optic modulator 2. The quality of the output waveform is improved by setting the appropriate rise time and opening time. The first thulium-doped fiber 4 is used as the main laser gain medium, and the thulium-doped fiber can generate laser in the 2um band. The first pump source 8 provides a 793nm laser to pump the first thulium-doped fiber, which matches the thulium-doped fiber and excites the thulium ions in the thulium-doped fiber. The 2x2 coupler 5 is used in the 2um Q-switched pulse fiber laser to effectively merge or distribute laser signals in different optical paths, provide flexible control of the light beam, ensure that the optical signals between the optical fibers in the seed source module can be effectively coupled, and improve the overall efficiency and performance of the system. The online isolator 9 is used to prevent the laser signal from backflowing and interfering with the laser. The second beam combiner 10 combines the light beams of the gain fiber. The second thulium-doped fiber 11 is used to further amplify the laser signal and increase the output power. The second pump source 13 provides the second thulium-doped fiber 11 with a laser of a pump matching wavelength. The amplifier module further amplifies the laser signal transmitted from the seed source module to increase the output power, and finally outputs a high peak power laser to the application end.

[0046] The laser of the invention has an operating wavelength of 1920-1950nm, a repetition frequency of 1kHz-50kHz, a pulse width of 40ns-100ns, a single pulse energy of 1mJ-2.5mJ, a peak power greater than 10kW, and an average power adjustable within the range of 1-100W.

[0047] As a preferred embodiment, the cavity length of the laser is 23-25m.

[0048] Appropriate cavity length helps stabilize the laser mode, reduce mode noise, and improve the laser beam quality. A longer cavity length can increase the laser optical path, allowing more gain media to participate in the laser process, thereby increasing the peak power and overall output power of the laser. In order to meet the needs of actual mass production, the cavity length of the laser is set to 23-25m, which can better match two pump sources with a wavelength of 793nm, and its output power and other parameters, to output pulsed lasers with preset waveforms.

[0049] As a preferred embodiment, the online isolator 9 is a double-stage online isolator with bandpass filtering, a central wavelength of 1940nm, and an average power of 10W.

[0050] The dual-stage in-line isolator with bandpass filtering, especially in the 1940nm center wavelength and 10W power range, can provide efficient optical isolation for lasers, optimize laser performance, enhance system stability, and improve the efficiency of the overall optical system.

[0051] As a preferred embodiment, the first beam combiner 3 adopts 10 / 130 input and 10 / 130 output. The first beam combiner keeps the same size of input and output beams, and performs preliminary beam combining to maintain beam quality.

[0052] The second beam combiner 10 adopts 10 / 130 input and 25 / 250 output. The 10 / 130 input port configuration is suitable for combining multiple beams into a single output, and the 25 / 250 output port provides higher output power and larger beam diameter, reduces the loss of beams in the beam combining process, and improves the utilization efficiency of beams.

[0053] By gradually combining the beams, the combination of the first beam combiner and the second beam combiner can effectively reduce the interference and distortion of the beams and optimize the quality and stability of the final beam.

[0054] As a preferred embodiment, the power distribution ratio of the 2*2 coupler 5 is 75 / 25.

[0055] The 75 / 25 split ratio can effectively deliver most of the power to the main output channel while directing less power to the auxiliary channel, suitable for applications that require high power output. By controlling the power split ratio, signal processing and transmission can be optimized, reducing power loss and signal interference in the optical system.

[0056] As a preferred embodiment, the reflectivity of the first high-reflectivity fiber Bragg grating 1 and the second high-reflectivity fiber Bragg grating 6 are both 99.9%.

[0057] As a preferred embodiment, a mode stripper is further provided between the second thulium-doped optical fiber 11 and the output jumper 12 .

[0058] Multimode interference may occur in thulium-doped fibers, which may affect the quality of the beam. Mode strippers can effectively remove these unwanted modes and reduce the impact of interference on the output signal. Before transmitting the fiber signal to the output jumper, the mode stripper can optimize the beam quality and ensure that the output optical signal has good transmission characteristics.

[0059] For the above laser, this embodiment also provides a 2um nanosecond pulse fiber laser time domain waveform adjustment method, which is applied to the 2um nanosecond pulse fiber laser described in any of the above technical solutions; the time domain waveform adjustment method includes:

[0060] Determining the driving rising edge time and the opening time of the acousto-optic modulator based on the cavity length of the laser and the frequency of the laser to be output;

[0061] Setting parameters of the acousto-optic modulator according to the rising edge time and the opening time;

[0062] The first pump source and the second pump source are turned on to output Q-switched pulse lasers that eliminate the multi-peak phenomenon.

[0063] Furthermore, the calculation method of the rising edge time s is:

[0064]

[0065] When the frequency increases, the number of particle inversions in the cavity decreases, and the rising edge time needs to be reduced to maintain a low pulse width.

[0066] The calculation method of the opening time T is:

[0067]

[0068] As the frequency increases, the number of particle inversions in the cavity decreases. At this time, the opening time is shortened to maintain a low pulse width. The pulse width of the laser output is within nanoseconds (10 -9 Seconds) level.

[0069] Where n is the refractive index of the optical fiber, c is the speed of light, l is the cavity length, f is the laser frequency, and A and B are both constants.

[0070] After setting the rising edge and the opening time, directly turn on the pump light to get a waveform without multiple peaks. The adjustment method is simple and fast, and there is no need to slowly adjust the cavity length, rising edge, and switching time, which saves a lot of debugging time and reduces manpower and material costs.

[0071] like Figure 2-4 As shown in the figure, the waveforms at different currents under the test frequency f = 30K, the test conditions are: cavity length l = 24.75m, fiber refractive index n = 1.48, light speed c = 2.99*10 8 , constant A = 3.67*10 -3 Constant B = 0.098.

[0072] By setting f = 30K, the rising edge time is s = 400ns, and the switching time is T = 3*10 -6 s, the waveforms when the current is 3A, 4A, and 5A are as follows Figure 2-Figure 4 As shown in the figure, it can be seen that under the three currents, the output waveform does not have multiple peaks, and the pulse width is low, which brings higher time resolution and stronger peak power.

[0073] In practical applications, it is only necessary to adjust the rising edge time s according to the frequency required for debugging, and then adjust the required opening time T according to the frequency and cavity length. After setting the rising edge and opening time, directly turn on the pump light to obtain a Q-switched laser pulse waveform without multi-peak phenomenon. There is no need to slowly adjust the cavity length, rising edge, and switching time, which saves a lot of debugging time and is convenient for actual mass production and use.

[0074] The 2um nanosecond pulse fiber laser and its adjustment method provided by the present invention use high reflectivity fiber grating and thulium-doped fiber to ensure the stability and efficient amplification of the laser mode. Through the cooperation of the acousto-optic modulator and the driving source, the rising edge time and the opening time can be accurately controlled, thereby improving the quality of the pulse waveform and reducing distortion and multi-peak phenomena. By optimizing the wavelength matching of the pump source and designing an efficient fiber combiner and isolator, it can better meet the needs of the 2um band, eliminate the multi-peak problem that may exist in the output pulse, increase the peak power and reduce the cost, and realize large-scale batch production.

[0075] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A 2um nanosecond pulse fiber laser, characterized in that: The pulse fiber laser comprises a seed source module and an amplification module connected to the seed source module; The seed source module includes a first high-reflectivity fiber Bragg grating, an acousto-optic modulator, a first beam combiner, a first thulium-doped fiber, a 2*2 coupler, and a second high-reflectivity fiber Bragg grating connected in sequence, and also includes a driving source connected to the acousto-optic modulator and a first pump source connected to the first beam combiner; The amplification module includes an online isolator, a second beam combiner, a second thulium-doped optical fiber and an output jumper connected in sequence, and a second pump source connected to the second beam combiner; The rising edge time and the opening time of the acousto-optic modulator are parameterized through the human-machine interface of the driving source; and the laser wavelengths output by the first pump source and the second pump source are both 793 nm.

2. The 2um nanosecond pulse fiber laser according to claim 1, characterized in that: The cavity length of the laser is 23-25m.

3. The 2um nanosecond pulse fiber laser according to claim 1, characterized in that: The online isolator is a double-stage online isolator with bandpass filtering.

4. The 2um nanosecond pulse fiber laser according to claim 1, characterized in that: The central wavelength of the online isolator is 1940nm and the average power is 10W.

5. The 2um nanosecond pulse fiber laser according to claim 1, characterized in that: The optical parameters of the first beam combiner are: 10 / 130 input and 10 / 130 output.

6. The 2um nanosecond pulse fiber laser according to claim 1, characterized in that: The optical parameters of the second beam combiner are: 10 / 130 input and 25 / 250 output.

7. The 2um nanosecond pulse fiber laser according to claim 1, characterized in that: The power distribution ratio of the 2*2 coupler is 75 / 25.

8. A time domain waveform adjustment method for a 2um nanosecond pulse fiber laser, characterized in that: The method is applied to the 2um nanosecond pulse fiber laser described in any one of claims 1 to 7; The time domain waveform adjustment method comprises: Determining the driving rising edge time and the opening time of the acousto-optic modulator based on the cavity length of the laser and the frequency of the laser to be output; Setting parameters of the acousto-optic modulator according to the rising edge time and the opening time; The first pump source and the second pump source are turned on to output Q-switched pulse lasers that eliminate the multi-peak phenomenon.

9. The method for adjusting the time domain waveform of a 2um nanosecond pulse fiber laser according to claim 8, characterized in that: The calculation method of the rising edge time s is: The calculation method of the opening time T is: Where n is the refractive index of the optical fiber, c is the speed of light, l is the cavity length, f is the laser frequency, and A and B are both constants.

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