High-power dual-frequency combined fiber laser amplification system with precise frequency shift and frequency shift method

Abstract

The invention relates to the technical field of photoelectron application, in particular to a high-power dual-frequency combined fiber laser amplification system with precise frequency shift and a frequency shift method, and aims to solve the problems that an existing traditional fiber laser frequency shift system is single in output waveform, limited in frequency regulation and control range and low in output energy. The high-power double-frequency combining optical fiber laser amplification system can output a laser pulse pair with randomly adjustable time waveform and certain energy by utilizing laser pulse balanced beam splitting, series-parallel connection of acousto-optic frequency shifters and a laser pulse precise beam combining technology, and the two laser pulses can be subjected to frequency shift respectively; the frequency difference between the two pulses can be accurately tuned in a wide range, and the technology has important application in the fields of spectral analysis, laser frequency stabilization, nonlinear optics and optical fiber communication.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic application technology, and in particular to a high-power dual-frequency combined fiber laser amplification system with precise frequency shifting and a frequency shifting method. Background Art

[0002] As an important part of contemporary laser science, fiber laser technology has shown its great application potential in many fields. Among them, the fiber laser amplification system with precisely adjustable frequency is a device that can be used to change the frequency of light waves, and has important applications in spectral analysis, laser frequency stabilization, nonlinear optics and fiber-optic communications.

[0003] However, the existing technology still has some deficiencies and disadvantages in the dual-frequency combined fiber laser amplification system and frequency shifting method:

[0004] Poor frequency stability: The traditional dual-frequency fiber laser amplification system has deficiencies in frequency stability. Due to environmental changes and the characteristics of the fiber itself, the laser frequency is prone to drift, resulting in a decrease in system performance.

[0005] Poor frequency shifting performance: The most widely used optical frequency shifters are based on acousto-optic modulators (AOM), also known as acousto-optic frequency shifters (AOFS). AOFS is mainly composed of RF drivers, ultrasonic transducers, acousto-optic crystals, ultrasonic energy absorbers, and fiber-coupled structures. Due to the size limitations of crystal materials, the frequency shift of acousto-optic devices is usually above tens of megahertz. In actual use, especially in heterodyne detection systems, the frequency shift of the laser is very small, often only a few megahertz or even lower, which cannot meet most application scenarios. In addition, the frequency control range is small, and the limited frequency shift range is generally between 40MHz and 300MHz.

[0006] Low output energy: During the dual-frequency combining process, due to the mutual interference of lasers of different frequencies and the transmission loss of optical fiber, it often leads to large energy loss, which reduces the output pulse energy of the system and results in low output energy.

[0007] Through the above analysis, the problems and defects of the existing technology are: due to environmental changes and the characteristics of the optical fiber itself, the laser frequency is prone to drift, resulting in a decrease in system performance; traditional AOFS has problems such as limited frequency control range, small frequency shift, and low output energy, which makes it difficult to meet the needs of complex application scenarios. Summary of the invention

[0008] The purpose of the present invention is to provide a high-power dual-frequency combined fiber laser amplification system with precise frequency shifting and a frequency shifting method, so as to solve the problems of single output waveform, limited frequency control range and low output energy of traditional fiber laser frequency shifting system.

[0009] To achieve the above object, the present invention provides a high-power dual-frequency combined fiber laser amplification system with precise frequency shifting, comprising:

[0010] A single longitudinal mode fiber laser for generating continuous light, an amplitude modulator for obtaining a shaped laser pulse by time-domain shaping of a small signal continuous light, a first fiber amplifier, an arbitrary waveform generator for generating an arbitrary electrical pulse signal, a first beam splitter, a first fiber acousto-optic modulator, a second fiber acousto-optic modulator, a 20 MHz frequency shifter, a 200 MHz frequency shifter, a third beam combiner, a second fiber amplifier, a third fiber acousto-optic modulator, and in addition to the optical path, a multi-channel synchronizer and a clock signal generator are included to provide a synchronization signal and a reference clock signal. The optical links are all transmitted using polarization-maintaining optical fibers;

[0011] The 20MHz frequency shifter is composed of a first beam combiner, a 180M fiber acousto-optic modulator, a first 200MHz fiber acousto-optic modulator, and a second beam splitter;

[0012] The 200 MHz frequency shifter is composed of a second beam combiner, a second 200 MHz fiber acousto-optic modulator, and a third beam splitter.

[0013] The multi-channel synchronizer is used to provide synchronization signals for the first fiber optic acousto-optic modulator, the second fiber optic acousto-optic modulator, the 180M fiber optic acousto-optic modulator, the first 200MHz fiber optic acousto-optic modulator, the second 200MHz fiber optic acousto-optic modulator, the third fiber optic acousto-optic modulator, the 20MHz frequency shifter, and the 200MHz frequency shifter;

[0014] The clock signal generator is used to provide a reference clock signal for the system.

[0015] Among them, a single longitudinal mode fiber laser, an amplitude modulator, a first fiber amplifier, a first beam splitter, a first fiber acousto-optic modulator, a first beam combiner, a 180M fiber acousto-optic modulator, a first 200MHz fiber acousto-optic modulator, a second beam splitter, a third beam combiner, a second fiber amplifier, and a second fiber acousto-optic modulator are connected in sequence.

[0016] Among them, a single longitudinal mode fiber laser, an amplitude modulator, a first fiber amplifier, a first beam splitter, a second fiber acousto-optic modulator, a second beam combiner, a second 200 MHz fiber acousto-optic modulator, a third beam splitter, a third beam combiner, a second fiber amplifier, and a second fiber acousto-optic modulator are connected in sequence.

[0017] The 20 MHz frequency shifter and the 200 MHz frequency shifter are respectively used to perform frequency shift operations of different frequencies on the laser pulses.

[0018] The 20MHz frequency shifter generates an adjustable positive frequency shift of 1 to 20MHz, and the 200MHz frequency shifter generates a fixed positive frequency shift of 200MHz.

[0019] The 20MHz frequency shifter can generate an adjustable positive frequency shift of 1 to 20MHz, that is, each time the laser pulse passes through the 20MHz frequency shifter, the laser frequency will shift 1 to 20MHz in the positive direction; therefore, the 20MHz frequency shifter can complete a frequency shift of up to 200MHz within 10 cycles, and the frequency shift range is 1 to 200MHz;

[0020] The 200MHz frequency shifter can generate a fixed 200MHz positive frequency shift, that is, each time the laser pulse passes through the 200MHz frequency shifter, the laser frequency will shift 200MHz in the positive direction. The 200MHz frequency shifter can complete a frequency shift of up to 2GHz within 10 cycles, and the frequency shift range is 200MHz to 2GHz;

[0021] In this system, after the 20MHz frequency shifter and the 200MHz frequency shifter are multiplexed in parallel, the frequency shift range is tunable in the range of 1MHz to 2.2GHz;

[0022] The laser pulse is transmitted from point A to point B, and the change in laser frequency is:

[0023]

[0024] Wherein, m is the number of times the laser pulse passes through the 20MHz frequency shifter, m = 1, 2, 3 ... 10; f is the frequency shift generated by a single pass through the 20MHz frequency shifter, f = 1, 2, 3 ... 20, unit MHz; n is the number of times the laser pulse passes through the 200MHz frequency shifter, n = 1, 2, 3 ... 10; ν c is the frequency shift produced by other acousto-optic crystals, in MHz. Then the frequency difference of the two pulses after beam combination is:

[0025] Δν= | 200N-MF | (2)

[0026] m and n can be set by a multi-channel synchronizer, and f can be set by the 20MHz frequency shifter; the frequency shift amount of the adjustable part depends on the number of times the optical pulse passes through the frequency shift device; the frequency shift device itself also has the function of an optical fiber acousto-optic modulator, which can control the time switching of the optical pulse under the control of the synchronization signal, thereby controlling the number of times the optical pulse passes through the frequency shift device;

[0027] In this system, after the 20 MHz frequency shifter and the 200 MHz frequency shifter are multiplexed in parallel, the frequency shift range is precisely tuned within the range of 1 MHz to 2.2 GHz.

[0028] The present invention also includes a frequency shifting method for a high-power dual-frequency combined fiber laser amplification system with precise frequency shifting:

[0029] The steps include:

[0030] An arbitrary waveform generator is used to generate an arbitrary electrical pulse signal injected into an amplitude modulator, thereby generating a pair of laser pulses that can be arbitrarily shaped;

[0031] A multi-channel synchronizer is used to provide synchronization signals for each fiber acousto-optic modulator and frequency shifter to control the number of times the laser pulse passes through the frequency shift device;

[0032] The two laser pulses are frequency-shifted at different frequencies by a 20MHz frequency shifter and a 200MHz frequency shifter, respectively, to achieve precise control of the frequency difference between the two pulses.

[0033] The optical fiber amplifier is used to amplify the energy of the frequency-shifted laser pulse until the output energy meets the preset requirements;

[0034] The dual-frequency combined laser pulses are beat and the frequency difference between the two laser pulses is measured to verify the frequency shift effect.

[0035] The pulse shape and pulse energy of the laser pulse output by the system are tested using an oscilloscope and an energy calorimeter to obtain the laser pulse characteristics output by the system.

[0036] The process of “beating the dual-frequency combined laser pulses and measuring the frequency difference between the two laser pulses to verify the frequency shift effect” includes the following steps:

[0037] Overlap two laser pulses in the time domain and observe the modulation-like phenomenon produced by the overlapping pulse flat tops in the oscilloscope. The frequency of the modulated waveform is the frequency difference between the two pulses.

[0038] The invention discloses a high-power dual-frequency combined fiber laser amplification system with precise frequency shifting, comprising: a single longitudinal mode fiber laser for generating continuous light, an amplitude modulator for obtaining a shaped laser pulse after time-domain shaping of a small signal continuous light, a first fiber amplifier, an arbitrary waveform generator for generating an arbitrary electrical pulse signal, a first beam splitter, a first fiber acousto-optic modulator, a second fiber acousto-optic modulator, a 20MHz frequency shifter, a 200MHz frequency shifter, a third beam combiner, a second fiber amplifier, and a third fiber acousto-optic modulator. In addition to the optical path, the system also comprises a multi-channel synchronizer and a clock signal generator for providing a synchronization signal and a reference clock signal. The optical links are all transmitted using polarization-maintaining optical fibers. The 200MHz frequency shifter is composed of a second beam combiner, a second 200MHz fiber acousto-optic modulator, and a third beam splitter. An electrical pulse signal for controlling the amplitude modulator to work is generated by an arbitrary waveform generator to generate a pair of laser pulses that can be arbitrarily shaped. The multi-channel synchronizer is used to synchronize the optical fibers. The acousto-optic modulator and frequency shifter provide synchronization signals to control the number of times the laser pulse passes through the frequency shifting device; the two laser pulses are frequency-shifted at different frequencies by a 20MHz frequency shifter and a 200MHz frequency shifter respectively to achieve precise control of the frequency difference between the two pulses; the energy of the frequency-shifted laser pulses is amplified by a fiber amplifier until the output energy meets the preset requirements; the dual-frequency combined laser pulses are beat and the frequency difference between the two laser pulses is measured to verify the frequency shifting effect; the pulse shape and pulse energy of the laser pulse output by the system are tested using an oscilloscope and an energy calorimeter to obtain the laser pulse characteristics output by the system. The high-power dual-frequency combined fiber laser amplification system can output a laser pulse pair with an arbitrarily adjustable time waveform and a certain energy by utilizing laser pulse balanced splitting, acousto-optic frequency shifters in series and parallel, and laser pulse precise combining technology. The two laser pulses can be frequency-shifted separately to make the frequency difference between the two pulses precisely tunable within a wide range. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0040] Figure 1 The high-power dual-frequency combined fiber laser amplification system of the present invention;

[0041] Figure 2 This is a schematic diagram of the laser pulse optical path transmission of the present invention;

[0042] Figure 3 It is the beat frequency pulse output by the high power dual frequency combined fiber laser amplification system;

[0043] Figure 4 This is a pulse energy diagram output by a high-power dual-frequency fiber laser amplification system.

[0044] Figure 5 The present invention is a flowchart of a frequency shifting method for a high-power dual-frequency combined fiber laser amplification system with precise frequency shifting.

[0045] In the figure: 1-single longitudinal mode fiber laser, 2-amplitude modulator, 3-first fiber amplifier, 4-arbitrary waveform generator, 5-first beam splitter, 6-first fiber acousto-optic modulator, 7-second fiber acousto-optic modulator, 8-first beam combiner, 9-second beam combiner, 10-180M fiber acousto-optic modulator, 11-first 200MHz fiber acousto-optic modulator, 12-second 200MHz fiber acousto-optic modulator, 13-second beam splitter, 14-third beam splitter, 15-third beam combiner, 16-second fiber amplifier, 17-third fiber acousto-optic modulator. In addition to the optical path, a multi-channel synchronizer and a clock signal generator are also included to provide synchronization signals and reference clock signals. DETAILED DESCRIPTION

[0046] Embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0047] Embodiment 1:

[0048] like Figure 1 As shown, a high-power dual-frequency combined fiber laser amplification system with precise frequency shift is provided, including a single longitudinal mode fiber laser 1 for generating continuous light, an amplitude modulator 2 for obtaining a shaped laser pulse after time-domain shaping of a small signal continuous light, a first fiber amplifier 3, an arbitrary waveform generator 4 for generating an arbitrary electrical pulse signal, a first beam splitter 5, a first fiber acousto-optic modulator 6, a second fiber acousto-optic modulator 7, a first beam combiner 8, a second beam combiner 9, a 180M fiber acousto-optic modulator 10, a first 200MHz fiber acousto-optic modulator 11, a second 200MHz fiber acousto-optic modulator 12, a second beam splitter 13, a third beam splitter 14, a third beam combiner 15, a second fiber amplifier 16, a third fiber acousto-optic modulator 17, a multi-channel synchronizer, and a clock signal generator. The 20MHz frequency shifter is composed of the first beam combiner 8, the 180M fiber acousto-optic modulator 10, the first 200MHz fiber acousto-optic modulator 11, and the second beam splitter 13. The 200 MHz frequency shifter is composed of a second beam combiner 9 , a second 200 MHz fiber acousto-optic modulator 12 , and a third beam splitter 14 .

[0049] Optical links all use polarization-maintaining optical fibers for transmission to ensure that the polarization state of the laser pulse does not change during transmission.

[0050] The high-power dual-frequency combined fiber laser amplification system with precision frequency shifting is characterized in that a single longitudinal mode fiber laser 1, an amplitude modulator 2, a first fiber amplifier 3, a first beam splitter 5, a first fiber acousto-optic modulator 6, a first beam combiner 8, a 180M fiber acousto-optic modulator 10, a first 200MHz fiber acousto-optic modulator 11, a second beam splitter 13, a third beam combiner 15, a second fiber amplifier 16, and a third fiber acousto-optic modulator 17 are sequentially connected through polarization-maintaining optical fibers.

[0051] The high-power dual-frequency combined fiber laser amplification system with precision frequency shifting is characterized in that a single longitudinal mode fiber laser 1, an amplitude modulator 2, a first fiber amplifier 3, a first beam splitter 5, a second fiber acousto-optic modulator 7, a second beam combiner 9, a second 200 MHz fiber acousto-optic modulator 12, a third beam splitter 14, a third beam combiner 15, a second fiber amplifier 16, and a third fiber acousto-optic modulator 17 are sequentially connected through polarization-maintaining optical fibers.

[0052] The first beam splitter 5, the second beam splitter 13 and the third beam splitter 14 are all 1×2 beam splitters; the first beam combiner 8, the second beam combiner 9 and the third beam combiner 15 are all 2×1 beam combiners.

[0053] The single longitudinal mode fiber laser 1 (DFB) is used to generate single longitudinal mode continuous laser, serving as the seed light source of the system, with an output power ≥ 20 mW;

[0054] The amplitude modulator 2 (AM) is used to perform amplitude modulation on the single longitudinal mode continuous laser to generate laser pulses that can be arbitrarily shaped;

[0055] The arbitrary waveform generator 4 (AWG) is used to generate an electrical pulse signal for controlling the operation of the amplitude modulator 2, thereby achieving precise control of the laser pulse waveform;

[0056] The 1×2 beam splitter is used to equally split the laser signal outputted by the front stage.

[0057] The multi-channel synchronizer is used to provide synchronization signals for each fiber optic acousto-optic modulator and 20MHz frequency shifter and 200MHz frequency shifter to ensure coordinated operation of various parts of the system;

[0058] The clock signal generator is used to provide a reference clock signal for the system;

[0059] The fiber acousto-optic modulator (AOM) is used to perform on-off control of the laser pulse in time, thereby controlling the number of times the light pulse passes through the frequency shift device;

[0060] The fiber amplifier (AMP) is used to amplify the energy of the laser pulse. In this system, two stages of AMP are used, and the output energy of the final stage of the system is ≥1nJ.

[0061] The 2×1 beam combiner combines two laser beams and has a reverse isolation function, so that the laser pulses are transmitted in one direction.

[0062] The 20MHz frequency shifter and the 200MHz frequency shifter are respectively used to perform frequency shift operations of different frequencies on the laser pulse;

[0063] The 20MHz frequency shifter is composed of a 180MHz fiber acousto-optic modulator and a 200MHz fiber acousto-optic modulator in cascade. The 20MHz frequency shifter can generate an adjustable positive frequency shift of 1 to 20MHz, that is, each time a laser pulse passes through the 20MHz frequency shifter, the laser frequency will move 1 to 20MHz in the positive direction; therefore, the 20MHz frequency shifter can complete a frequency shift of up to 200MHz within 10 cycles, and the frequency shift range is 1 to 200MHz.

[0064] The 200MHz frequency shifter can generate a fixed 200MHz positive frequency shift, that is, each time the laser pulse passes through the 200MHz frequency shifter, the laser frequency will shift 200MHz in the positive direction. Therefore, the 200MHz frequency shifter can complete a maximum frequency shift of 2GHz within 10 cycles, and the frequency shift range is 200MHz to 2GHz.

[0065] The system controls the cycle periods of the 20 MHz frequency shifter and the 200 MHz frequency shifter to within 10 in order to avoid amplitude instability caused by a large number of cycles.

[0066] In this system, after the 20MHz frequency shifter and the 200MHz frequency shifter are multiplexed in parallel, the frequency shift range is tunable in the range of 1MHz to 2.2GHz.

[0067] Embodiment 2:

[0068] The high-power dual-frequency combined fiber laser amplification system uses the frequency shift characteristics of the acousto-optic crystal to achieve frequency shift adjustment of the laser pulse signal. The optical pulse signal will shift in frequency when it is transmitted in the ring optical path of the frequency shifter. The optical path is calculated based on the cycle period to determine the frequency shift frequency of the pulse signal. The frequency shift frequency of the output optical pulse signal can be determined by controlling the switching time of the fiber acousto-optic modulator.

[0069] The 20MHz frequency shifter is composed of a 180MHz fiber acousto-optic modulator and a 200MHz acousto-optic modulator in cascade. The 20MHz frequency shifter can produce an adjustable positive frequency shift of 1 to 20MHz, that is, each time the laser pulse passes through the 20MHz frequency shifter, the laser frequency will shift 1 to 20MHz in the positive direction; therefore, the 20MHz frequency shifter can complete a frequency shift of up to 200MHz within 10 cycles, and the frequency shift range is 1 to 200MHz. The 200MHz frequency shifter can complete a frequency shift of up to 2GHz within 10 cycles, and the frequency shift range is 200MHz to 2GHz.

[0070] System optical path Figure 1 As shown, the laser pulse is transmitted from point A to point B, and the change in laser frequency is:

[0071]

[0072] Wherein, m is the number of times the laser pulse passes through the 20MHz frequency shifter, m = 1, 2, 3 ... 10; f is the frequency shift generated by a single pass through the 20MHz frequency shifter, f = 1, 2, 3 ... 20, unit MHz; n is the number of times the laser pulse passes through the 200MHz frequency shifter, n = 1, 2, 3 ... 10; ν c is the frequency shift produced by other acousto-optic crystals, in MHz. Then the frequency difference of the two pulses after beam combination is:

[0073] Δν= | 200N-MF | (2)

[0074] In actual operation, m and n can be set by a multi-channel synchronizer, and f can be set by a 20MHz frequency shifter. The frequency shift amount of the adjustable part depends on the number of times the light pulse passes through the frequency shift device. The frequency shift device itself also has the function of a fiber optic acousto-optic modulator, which can control the time switching of the light pulse under the control of the synchronization signal, thereby realizing the control of the number of times the light pulse passes through the frequency shift device.

[0075] Therefore, in this system, after the 20MHz frequency shifter and the 200MHz frequency shifter are multiplexed in parallel, the frequency shift range is accurately tuned within the range of 1MHz to 2.2GHz.

[0076] Embodiment three:

[0077] Based on Examples 1 and 2, this embodiment further provides a beat frequency step to test the frequency shift effect. Specifically, two laser pulses are overlapped in the time domain, and the modulation-like phenomenon generated by the overlapping pulse flat tops in the oscilloscope is observed. By measuring the frequency of the modulated waveform, the frequency difference between the two laser pulses can be obtained, thereby testing the frequency shift effect.

[0078] like Figure 2 The figure shows the transmission process of two pulses performing beat frequency in the optical path. The transmission route of the first pulse is C→D1→E, and the transmission route of the second pulse is C→D2→E. When observing at point A, the optical path is not split at this time, and there is a certain delay difference between the two pulses. Since the optical fiber lengths of the two transmission routes C→D1→E and C→D2→E are not the same (the lengths of the optical fiber jumpers are different, and the optical fiber lengths of different devices are also different), and the frequency shifter will also change the timing position of the optical pulse when shifting the frequency of the optical pulse, the delay difference between the two pulses must have changed when observing at point C. In order to make the two pulses overlap in the time domain Figure 2 The "modulation" phenomenon shown at point C (i.e., the occurrence of beat frequency) requires modulating the timing of the multi-channel synchronizer so that the delay difference between the two pulses at point C is offset, thereby achieving overlap of the two pulses in the time domain. Ultimately, the beat frequency pulse is observed. By measuring the frequency of the beat frequency output waveform, the frequency difference between the two laser pulses can be obtained, thereby verifying the frequency shift effect.

[0079] like Figure 3 The figure shows the beat frequency pulse output by the high-power dual-frequency combined fiber laser amplification system. The frequency shift of the frequency-shifted pulse is measured on an oscilloscope.

[0080] like Figure 4 The figure shows the pulse energy diagram of the high-power dual-frequency combined fiber laser amplification system. The pulse energy is 1.229nJ and the pulse energy instability is 0.821%, which proves that the system has stable output pulse energy and high stability.

[0081] like Figure 5 The figure shows a frequency shifting method of a high-power dual-frequency combined fiber laser amplification system with precise frequency shifting, comprising the following steps:

[0082] S1: Generate an arbitrary electrical pulse signal injected into the amplitude modulator through an arbitrary waveform generator to produce a laser pulse pair that can be arbitrarily shaped;

[0083] S2: Use a multi-channel synchronizer to provide synchronization signals for each fiber acousto-optic modulator and frequency shifter to control the number of times the laser pulse passes through the frequency shift device;

[0084] S3: The two laser pulses are frequency-shifted at different frequencies by a 20MHz frequency shifter and a 200MHz frequency shifter, respectively, to achieve precise control of the frequency difference between the two pulses.

[0085] S4: using a fiber amplifier to amplify the energy of the frequency-shifted laser pulse until the output energy meets the preset requirements;

[0086] S5: Beat the dual-frequency combined laser pulses and measure the frequency difference between the two laser pulses to verify the frequency shift effect;

[0087] S6: Use an oscilloscope and an energy calorimeter to test the pulse shape and pulse energy of the laser pulse output by the system, and obtain the laser pulse characteristics of the system output.

[0088] In this embodiment:

[0089] 1. Generate an arbitrary electrical pulse signal injected into the amplitude modulator 2 through the arbitrary waveform generator 4 to generate a laser pulse pair that can be arbitrarily shaped;

[0090] 2. Use a multi-channel synchronizer to provide synchronization signals for each fiber acousto-optic modulator and frequency shifter to control the number of times the laser pulse passes through the frequency shift device;

[0091] 3. Use a 20MHz frequency shifter and a 200MHz frequency shifter to perform frequency shift operations on the two laser pulses at different frequencies, so as to achieve precise control of the frequency difference between the two pulses;

[0092] 4. Use the optical fiber amplifier to amplify the energy of the frequency-shifted laser pulse to ensure that the output energy meets the requirements;

[0093] 5. Beat the dual-frequency combined laser pulses to measure the frequency difference between the two laser pulses to verify the frequency shift effect; the beat step includes: overlapping the two laser pulses in the time domain, observing the modulation phenomenon generated by the overlapping pulse flat tops in the oscilloscope, and the frequency of the modulated waveform is the frequency difference between the two pulses;

[0094] 6. Finally, use an oscilloscope and energy calorimeter to test the pulse shape and pulse energy of the laser pulse output by the system to obtain the laser pulse characteristics of the system output.

[0095] The beneficial effects of the present invention are:

[0096] 1. The present invention provides a high-power dual-frequency combined fiber laser amplification system with precise frequency shifting, which can output laser pulse pairs with a certain energy and an adjustable time waveform, and realize precise control of the frequency difference between the two pulses, meeting the needs of complex application scenarios;

[0097] 2. The frequency shifting method of the present invention realizes precise control of the frequency difference between two laser pulses by controlling the number of times the laser pulse passes through the frequency shifting device and the setting parameters of the frequency shifter, and has the advantages of a large control range and high precision;

[0098] 3. The present invention also provides a frequency shifting method and a frequency beating step for achieving accurate frequency shifting and measuring the frequency difference between two laser pulses to verify the frequency shifting effect;

[0099] 4. The DFB, AM, AOM, AMP, 20MHz frequency shifter, and 200MHz frequency shifter are all modular plug-in structures, which are conducive to system maintenance and integrated installation and debugging, and the optical path cascades between the module plug-ins are all connected by high-precision flanges to effectively reduce polarization mode dispersion. In addition, by adopting a fully polarization-maintaining fiber optical path structure, the laser signal is transmitted along the optical link with polarization maintenance, making the performance of the laser pulse more stable and reliable.

[0100] What is disclosed above is only one or more preferred embodiments of the present application, and cannot be used to limit the scope of rights of the present application. Ordinary technicians in this field can understand that all or part of the processes of implementing the above embodiments and equivalent changes made according to the claims of the present application are still within the scope covered by the present application.

Claims

1. A high-power dual-frequency combined fiber laser amplification system with precise frequency shifting, characterized in that: include: A single longitudinal mode fiber laser for generating continuous light, an amplitude modulator for obtaining a shaped laser pulse by time-domain shaping of a small signal continuous light, a first fiber amplifier, an arbitrary waveform generator for generating an arbitrary electrical pulse signal, a first beam splitter, a first fiber acousto-optic modulator, a second fiber acousto-optic modulator, a 20 MHz frequency shifter, a 200 MHz frequency shifter, a third beam combiner, a second fiber amplifier, a third fiber acousto-optic modulator, and in addition to the optical path, a multi-channel synchronizer and a clock signal generator are included to provide a synchronization signal and a reference clock signal. The optical links are all transmitted using polarization-maintaining optical fibers; The 20MHz frequency shifter is composed of a first beam combiner, a 180M fiber acousto-optic modulator, a first 200MHz fiber acousto-optic modulator, and a second beam splitter; The 200 MHz frequency shifter is composed of a second beam combiner, a second 200 MHz fiber acousto-optic modulator, and a third beam splitter.

2. The high-power dual-frequency combined fiber laser amplification system with precise frequency shifting as claimed in claim 1, characterized in that: The multi-channel synchronizer is used to provide synchronization signals for the first fiber optic acousto-optic modulator, the second fiber optic acousto-optic modulator, the 180M fiber optic acousto-optic modulator, the first 200MHz fiber optic acousto-optic modulator, the second 200MHz fiber optic acousto-optic modulator, the third fiber optic acousto-optic modulator, the 20MHz frequency shifter, and the 200MHz frequency shifter; The clock signal generator is used to provide a reference clock signal for the system. The third fiber acousto-optic modulator is used to further suppress the noise of the laser pulse output by the previous stage.

3. The high-power dual-frequency combined fiber laser amplification system with precise frequency shifting as claimed in claim 2, characterized in that: A single longitudinal mode fiber laser, an amplitude modulator, a first fiber amplifier, a first beam splitter, a first fiber acousto-optic modulator, a first beam combiner, a 180M fiber acousto-optic modulator, a first 200MHz fiber acousto-optic modulator, a second beam splitter, a third beam combiner, a second fiber amplifier, and a second fiber acousto-optic modulator are connected in sequence.

4. The high-power dual-frequency combined fiber laser amplification system with precise frequency shifting as claimed in claim 1, characterized in that: A single longitudinal mode fiber laser, an amplitude modulator, a first fiber amplifier, a first beam splitter, a second fiber acousto-optic modulator, a second beam combiner, a second 200 MHz fiber acousto-optic modulator, a third beam splitter, a third beam combiner, a second fiber amplifier, and a second fiber acousto-optic modulator are connected in sequence.

5. The high-power dual-frequency combined fiber laser amplification system with precise frequency shifting as claimed in claim 4, characterized in that: The 20 MHz frequency shifter and the 200 MHz frequency shifter are respectively used to perform frequency shift operations of different frequencies on laser pulses.

6. The high-power dual-frequency combined fiber laser amplification system with precise frequency shifting as claimed in claim 5, characterized in that: The 20MHz frequency shifter can generate an adjustable positive frequency shift of 1 to 20MHz, that is, each time the laser pulse passes through the 20MHz frequency shifter, the laser frequency will shift 1 to 20MHz in the positive direction; therefore, the 20MHz frequency shifter can complete a frequency shift of up to 200MHz within 10 cycles, and the frequency shift range is 1 to 200MHz; The 200MHz frequency shifter can generate a fixed 200MHz positive frequency shift, that is, each time the laser pulse passes through the 200MHz frequency shifter, the laser frequency will shift 200MHz in the positive direction. The 200MHz frequency shifter can complete a frequency shift of up to 2GHz within 10 cycles, and the frequency shift range is 200MHz to 2GHz; In this system, after the 20MHz frequency shifter and the 200MHz frequency shifter are multiplexed in parallel, the frequency shift range is tunable in the range of 1MHz to 2.2GHz; The laser pulse is transmitted from point A to point B, and the change in laser frequency is: Wherein, m is the number of times the laser pulse passes through the 20MHz frequency shifter, m = 1, 2, 3 ... 10; f is the frequency shift generated by a single pass through the 20MHz frequency shifter, f = 1, 2, 3 ... 20, unit MHz; n is the number of times the laser pulse passes through the 200MHz frequency shifter, n = 1, 2, 3 ... 10; ν c is the frequency shift produced by other acousto-optic crystals, in MHz. Then the frequency difference of the two pulses after beam combination is: Δν= | 200n-mf | (2) m and n can be set by a multi-channel synchronizer, and f can be set by the 20MHz frequency shifter; the frequency shift amount of the adjustable part depends on the number of times the optical pulse passes through the frequency shift device; the frequency shift device itself also has the function of an optical fiber acousto-optic modulator, which can control the time switching of the optical pulse under the control of the synchronization signal, thereby controlling the number of times the optical pulse passes through the frequency shift device; In this system, after the 20 MHz frequency shifter and the 200 MHz frequency shifter are multiplexed in parallel, the frequency shift range is precisely tuned within the range of 1 MHz to 2.2 GHz.

7. A frequency shifting method for a high-power dual-frequency combined fiber laser amplification system with precision frequency shifting, applicable to the high-power dual-frequency combined fiber laser amplification system with precision frequency shifting as claimed in any one of claims 1 to 6, characterized in that: The steps include: An arbitrary waveform generator is used to generate an arbitrary electrical pulse signal injected into the amplitude modulator to produce a pair of laser pulses that can be arbitrarily shaped; A multi-channel synchronizer is used to provide synchronization signals for each fiber acousto-optic modulator and frequency shifter to control the number of times the laser pulse passes through the frequency shift device; The two laser pulses are frequency-shifted at different frequencies by a 20MHz frequency shifter and a 200MHz frequency shifter, respectively, to achieve precise control of the frequency difference between the two pulses. The optical fiber amplifier is used to amplify the energy of the frequency-shifted laser pulse until the output energy meets the preset requirements; The dual-frequency combined laser pulses are beat and the frequency difference between the two laser pulses is measured to verify the frequency shift effect; The pulse shape and pulse energy of the laser pulse output by the system are tested using an oscilloscope and an energy calorimeter to obtain the laser pulse characteristics output by the system.

8. The frequency shifting method of the high-power dual-frequency combined fiber laser amplification system with precise frequency shifting as claimed in claim 7, characterized in that: In "beating the dual-frequency combined laser pulses and measuring the frequency difference between the two laser pulses to verify the frequency shift effect", the following steps are included: Overlap two laser pulses in the time domain and observe the modulation-like phenomenon produced by the overlapping pulse flat tops in the oscilloscope. The frequency of the modulated waveform is the frequency difference between the two pulses.

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