High repetition rate mid-infrared waveband pulsed light source based on parametric down conversion and generation method

Abstract

The application relates to a mid-infrared waveband pulsed light source and a generating method, in particular to a high-repetition-frequency mid-infrared waveband pulsed light source based on parametric down conversion and a generating method, which is used to solve the problems that the traditional mid-infrared waveband pulsed light source adopts a mid-infrared direct mode-locked scheme, is restricted by low power and line width difference, and results in a large overall system volume, a complex structure, a complex light source structure based on cross-frequency-band wavelength conversion from near-infrared to mid-infrared, high cost, and high professional requirement for operators. The high-repetition-frequency mid-infrared waveband pulsed light source based on parametric down conversion comprises a pump laser unit, a pulse generation unit, a pulse output unit and a state judgment unit.

Description

TECHNICAL FIELD

[0001] The present application relates to a mid-infrared waveband pulsed light source and a generating method, in particular to a high-repetition-rate mid-infrared waveband pulsed light source and a generating method based on parametric down-conversion. BACKGROUND

[0002] The mid-infrared waveband is an important atmospheric window and is matched with heat sources such as engines and power facilities, and has important applications in the fields of spectroscopy, remote sensing and communication. Compared with mid-infrared continuous wave lasers, mid-infrared pulsed laser light sources have a wide spectral coverage and high instantaneous peak power, and are extremely easy to cause instantaneous saturation of optoelectronic devices when interacting with the optoelectronic devices, and therefore are of great significance.

[0003] Traditional mid-infrared waveband pulsed lasers are usually generated by modulating a mid-infrared waveband narrow-linewidth continuous wave laser source (such as an optical parametric oscillator (OPO) light source or a quantum cascade laser (QCL)) with a pump nonlinear crystal or a saturable absorber (SESAM, Cr:ZnS, etc.). Due to the limitations of device performance and generation technology, the current mid-infrared continuous wave laser sources are restricted by low power and wide linewidth difference, resulting in a large overall system size and complex structure. At the same time, due to the long optical path and numerous devices in the system, the coupling loss is large and the repetition rate (referred to as repetition rate) is low, and the development of mid-infrared pulsed laser light sources, especially in the 3 μm and above waveband, is slow, which cannot meet the needs of space communication for large frequency band intervals (i.e. high repetition rate) and spectral detection for large bandwidth range.

[0004] Compared with the above, the continuous and pulsed light source technology in the near-infrared waveband is very mature, and has high output power, wide tuning range and many supporting devices, and therefore if the mid-infrared pulsed laser can be generated by using the near-infrared laser with advanced performance, the above-mentioned restrictive problems can be solved.

[0005] The cross-band wavelength conversion from near-infrared to mid-infrared can be realized by using a traditional bulk crystal, but in general, the conversion efficiency is low and the threshold requirement is high, and the efficiency of the nonlinear process needs to be greatly improved. In addition, the refractive index difference of the same crystal at different wavebands is large and the group velocity dispersion is easily mismatched. The above problems result in a complex structure and high cost of the light source based on the cross-band wavelength conversion from near-infrared to mid-infrared, and the professional requirements for the operating personnel are extremely high. SUMMARY

[0006] The purpose of the present application is to solve the problems of the traditional mid-infrared pulsed light source, which uses a mid-infrared direct mode-locked scheme, is restricted by low power and wide linewidth difference, results in a large overall system size and complex structure, and the light source based on the cross-band wavelength conversion from near-infrared to mid-infrared has a complex structure, high cost and extremely high professional requirements for the operating personnel, and to provide a high-repetition-rate mid-infrared waveband pulsed light source and a generating method based on parametric down-conversion.

[0007] To solve the above problems existing in the prior art, the present application provides the following technical solutions:

[0008] A high-repetition-rate mid-infrared waveband pulsed light source based on parametric down-conversion, characterized in that it comprises a pump laser unit, a pulse generation unit, a pulse output unit and a state determination unit connected in sequence.

[0009] The pump laser unit is configured to generate near-infrared pump laser pulses.

[0010] The pulse generation unit is configured to realize frequency conversion from near-infrared to mid-infrared waveband through a second-order nonlinear parametric down-conversion process, and further realize spectral broadening through a third-order nonlinear cascaded four-wave mixing process, thereby generating mid-infrared waveband pulsed laser.

[0011] The pulse output unit is configured to filter out residual near-infrared pump laser pulses in the mid-infrared waveband pulsed laser, and then inject the mid-infrared waveband pulsed laser into the state determination unit after beam splitting.

[0012] The state determination unit is configured to monitor power dynamic changes and output pulse spectral characteristics, and provide feedback basis for work state regulation of the pump laser unit and the pulse generation unit.

[0013] Further, the pump laser unit comprises a near-infrared pulsed laser, a fiber amplifier and a lens fiber connected in sequence; the near-infrared pulsed laser is configured to generate near-infrared pump laser pulses; the fiber amplifier is configured to amplify the intensity of the near-infrared pump laser pulses; and the lens fiber is configured to compress the mode field of the near-infrared pump laser pulses and inject them into the pulse generation unit.

[0014] Further, the pulse generation unit comprises a micro-ring resonant cavity chip and a direct current power supply; the micro-ring resonant cavity chip comprises a common waveguide, a micro-ring resonant cavity waveguide and a metal hot electrode; the input port of the common waveguide is connected to the output end of the lens fiber, and the output port of the common waveguide is connected to the input end of the pulse output unit; the positive and negative electrodes of the direct current power supply are connected to the metal hot electrode, and the direct current power supply is configured to change the working temperature of the micro-ring resonant cavity chip and tune the actual cavity length of the micro-ring resonant cavity chip.

[0015] Further, the micro-ring resonant cavity chip is made of one of lithium niobate, gallium arsenide aluminum, aluminum nitride and gallium nitride.

[0016] Further, the pulse output unit comprises, in sequence along the light path, a microscope objective, a band-pass filter, a beam splitter and a mirror; the input end of the microscope objective is connected with the output port of the common waveguide; the beam splitter is used for splitting the mid-infrared waveband pulse laser into a first pulse and a second pulse; the first pulse is directly output to the state judgment unit by the beam splitter; and the second pulse is output to the state judgment unit after being reflected by the mirror.

[0017] Further, the state judgment unit comprises a power meter and a spectrometer; the power meter is used for receiving the first pulse to monitor the power dynamic change of the mid-infrared waveband pulse laser; and the spectrometer is used for receiving the second pulse to analyze the spectral characteristics of the mid-infrared waveband pulse laser.

[0018] Meanwhile, the application also provides a high-repetition-rate mid-infrared waveband pulse generation method based on parametric down-conversion, which is characterized by using the above-mentioned high-repetition-rate mid-infrared waveband pulse source based on parametric down-conversion, and comprises the following steps:

[0019] Step 1: making the pump laser unit generate near-infrared pump laser pulses, and tuning the output power of the near-infrared pump laser pulses so that the intensity of the output near-infrared pump laser pulses exceeds the threshold value of the parametric down-conversion process of the pulse generation unit;

[0020] Step 2: adjusting the working temperature of the pulse generation unit so that the pulse generation unit generates the parametric down-conversion process of the second-order nonlinearity at the working temperature to realize the frequency conversion from near-infrared to mid-infrared waveband, and realizes the spectral expansion through the cascade four-wave mixing process of the third-order nonlinearity to generate mid-infrared waveband pulse laser;

[0021] Step 3: filtering out the residual near-infrared pump laser pulses in the mid-infrared waveband pulse laser through the pulse output unit, and then dividing the mid-infrared waveband pulse laser into a first pulse and a second pulse, and respectively injecting them into the state judgment unit;

[0022] Step 4: monitoring the power dynamic change of the mid-infrared waveband pulse laser and the spectral characteristics of the mid-infrared waveband pulse laser through the state judgment unit according to the first pulse and the second pulse respectively, and adjusting the pump laser unit and the pulse generation unit according to the monitoring results until the monitoring results show that the mid-infrared waveband pulse laser meets the preset requirements, so as to realize the generation of high-repetition-rate mid-infrared waveband pulse.

[0023] Further, the step 1 is specifically: generating the near-infrared pump laser pulses through a near-infrared pulse laser, and simultaneously tuning the output power of the fiber amplifier so that the intensity of the output near-infrared pump laser pulses exceeds the threshold value of the parametric down-conversion process of the micro-ring resonant cavity chip after amplification.

[0024] Further, the step 2 is specifically: changing the working temperature of the micro-ring resonator cavity chip by tuning the output current or voltage of the direct current power supply, so that the micro-ring resonator cavity chip undergoes parametric down-conversion process at the working temperature to realize frequency conversion from near-infrared to mid-infrared waveband, and the frequency spectrum is expanded through a cascade four-wave mixing process of third-order nonlinearity, thereby generating mid-infrared waveband pulsed laser.

[0025] Further, the step 4 is specifically:

[0026] Step 4.1, receiving the first pulse through the power meter, monitoring the power dynamic change of the mid-infrared waveband pulsed laser, and adjusting the output current or voltage of the direct current power supply until the power of the mid-infrared waveband pulsed laser reaches the maximum value, and then maintaining the output current or voltage of the direct current power supply unchanged;

[0027] Step 4.2, receiving the second pulse through the spectrometer, monitoring the spectral characteristics of the mid-infrared waveband pulsed laser, and adjusting the output power of the fiber amplifier until the spectral envelope is stable and the bandwidth reaches the maximum, and then maintaining the output power of the fiber amplifier unchanged.

[0028] Compared with the prior art, the present application has the following advantages:

[0029] (1) The present application is a high-repetition-rate mid-infrared waveband pulsed light source based on parametric down-conversion, which comprises a pump laser unit, a pulse generation unit, a pulse output unit and a state determination unit. The present application uses a mature near-infrared pulsed laser integrated micro-ring resonator cavity chip, realizes initial frequency conversion from near-infrared to mid-infrared through a second-order nonlinear parametric down-conversion process, and further expands the frequency through a cascade four-wave mixing process of third-order nonlinearity. The second-order and third-order nonlinear effects can be fully utilized to generate high-efficiency, large-bandwidth mid-infrared waveband pulsed laser with low threshold requirement and required near-infrared pulsed laser peak power < 50W. Therefore, common near-infrared pulsed lasers can meet the requirements and have strong practicability.

[0030] (2) The present application is a high-repetition-rate mid-infrared waveband pulsed generation method based on parametric down-conversion. The method realizes high-repetition-rate mid-infrared waveband pulsed laser by using near-infrared pulsed parametric down-conversion, which breaks through the limitations of pump light source output power and tuning performance faced by traditional mid-infrared direct mode-locked scheme, and overcomes the constraints of large size and high cost. The present application has simple structure, easy implementation and wide application value.

[0031] (3) The application is a high-repetition mid-infrared pulse generation method based on parametric down conversion, which uses a micro-ring resonator chip to realize high-repetition mid-infrared pulse generation, fully utilizes the strong resonance capability and small cavity length of the micro-ring resonator chip, and has the characteristics of low pump threshold, high repetition frequency and large spectral bandwidth. The generated mid-infrared pulse laser has a spectral width of >600 nm and a repetition frequency of >50 GHz.

[0032] (4) The application is a high-repetition mid-infrared pulse generation method based on parametric down conversion, which uses a near-infrared pulse laser to replace a mid-infrared narrow linewidth light source to pump a micro-ring resonator chip. The near-infrared band has rich supporting devices and supports fiber coupling, so the coupling efficiency can be improved and the system size can be reduced, further improving the integration level.

[0033] (5) The application is a high-repetition mid-infrared pulse generation method based on parametric down conversion, which monitors the power dynamic change of the mid-infrared pulse laser to determine the working state of the high-repetition mid-infrared pulse laser source, and adjusts the micro-ring resonator chip temperature to finely adjust the micro-ring resonator chip cavity length, thereby solving the problem of pump pulse and microcavity repetition frequency mismatch, and difficult to efficiently synchronize pumping. It has the advantages of flexible control and simple operation.

[0034] (6) In the high-repetition mid-infrared pulse source based on parametric down conversion, the preparation material of the micro-ring resonator chip can be a variety of different materials that are transparent from near-infrared to mid-infrared band and have negative dispersion, as well as second-order and third-order nonlinear effects, and supports different pump laser pulses (active modulation or passive lock model), so the application range is wide and the versatility is strong. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 It is a structure schematic diagram of the high-repetition mid-infrared pulse source based on parametric down conversion of the application;

[0036] Figure 2 It is an initial spectrum schematic diagram of the near-infrared pump laser pulse generated in step 1 of the high-repetition mid-infrared pulse generation method based on parametric down conversion of the application;

[0037] Figure 3 It is a time-domain waveform schematic diagram of the near-infrared pump laser pulse generated in step 1 of the high-repetition mid-infrared pulse generation method based on parametric down conversion of the application;

[0038] Figure 4 It is a schematic diagram of the parametric down conversion process of the near-infrared pump laser pulse in step 2 of the high-repetition mid-infrared pulse generation method based on parametric down conversion of the application; (2) ​

[0039] Figure 5 A schematic diagram of a four-wave mixing process for further expanding the spectrum to both sides for the frequency of the mid-infrared waveband in step 2 of the embodiment of the method for generating mid-infrared waveband pulses based on parametric down-conversion of the application; (3) A schematic diagram of a four-wave mixing process for further expanding the spectrum to both sides for the frequency of the mid-infrared waveband in step 2 of the embodiment of the method for generating mid-infrared waveband pulses based on parametric down-conversion of the application;

[0040] Figure 6 A schematic diagram of the spectral shape of the mid-infrared waveband pulse laser generated by the embodiment of the method for generating mid-infrared waveband pulses based on parametric down-conversion of the application;

[0041] Figure 7 A schematic diagram of the time-domain waveform of the mid-infrared waveband pulse laser generated by the embodiment of the method for generating mid-infrared waveband pulses based on parametric down-conversion of the application.

[0042] The reference signs are explained as follows: 1 - near-infrared pulse laser; 2 - fiber amplifier; 3 - lens fiber; 4 - micro-ring resonator chip; 5 - direct-current power supply; 6 - microscope objective; 7 - bandpass filter; 8 - beam splitter; 9 - mirror; 10 - power meter; 11 - spectrometer; 41 - input port of common waveguide; 42 - output port of common waveguide; 43 - micro-ring resonator waveguide; 44 - metal hot electrode. DETAILED DESCRIPTION

[0043] The application will be further described below in conjunction with the drawings and exemplary embodiments.

[0044] Reference Figure 1 A high-repetition-rate mid-infrared waveband pulse light source based on parametric down-conversion, comprising a pump laser unit, a pulse generation unit, a pulse output unit and a state determination unit connected in sequence.

[0045] The pump laser unit is used to generate near-infrared pump laser pulses, and comprises a near-infrared pulse laser 1, a fiber amplifier 2 and a lens fiber 3 connected in sequence; the near-infrared pulse laser 1 is used to generate near-infrared pump laser pulses; the fiber amplifier 2 is used to amplify the intensity of the near-infrared pump laser pulses; and the lens fiber 3 is used to compress the mode field of the near-infrared pump laser pulses and inject them into the pulse generation unit.

[0046] The pulse generation unit is used for realizing frequency conversion from near-infrared to mid-infrared wave band through a parametric down-conversion process of a second-order nonlinearity, and realizing further spectrum expansion through a cascaded four-wave mixing process of a third-order nonlinearity, and then generating mid-infrared wave band pulse laser; the pulse generation unit comprises a micro-ring resonant cavity chip 4 and a direct current power supply 5; the micro-ring resonant cavity chip 4 comprises a common waveguide, a micro-ring resonant cavity waveguide 43 and a metal hot electrode 44; an input port 41 of the common waveguide is connected with an output end of the lens optical fiber 3, and an output port 42 of the common waveguide is connected with an input end of the pulse output unit; positive and negative poles of the direct current power supply 5 are connected on the metal hot electrode 44, and the direct current power supply 5 is used for changing the working temperature of the micro-ring resonant cavity chip 4, and tuning the actual cavity length of the micro-ring resonant cavity chip 4.

[0047] The preparation material of the micro-ring resonant cavity chip 4 in the embodiment is required to be transparent from near-infrared to mid-infrared wave band, have negative dispersion, and have second-order and third-order nonlinearity effects, for example, one of lithium niobate (LiNbO3), gallium aluminum arsenide (AlGaAs), aluminum nitride (AlN) and gallium nitride (GaN).

[0048] In the micro-ring resonant cavity chip 4 used in the embodiment, the metal hot electrode 44 is arranged above the periphery of the micro-ring resonant cavity waveguide 43, and in other embodiments, a whole heating / cooling mode of placing a semiconductor thermoelectric cooling piece (TEC) at the bottom of the micro-ring resonant cavity chip 4 can also be used to realize temperature tuning of the micro-ring resonant cavity waveguide 43.

[0049] The pulse output unit is used for filtering residual near-infrared pump laser pulses in the mid-infrared wave band pulse laser, and then injecting the mid-infrared wave band pulse laser into the state judgment unit after beam splitting; the pulse output unit comprises a microscopic objective lens 6, a band-pass filter 7, a beam splitter 8 and a reflector 9 arranged in sequence along an optical path; an input end of the microscopic objective lens 6 is connected with the output port 42 of the common waveguide, the beam splitter 8 is used for splitting the mid-infrared wave band pulse laser into a first pulse and a second pulse, the first pulse is directly output to the state judgment unit by the beam splitter 8, and the second pulse is output to the state judgment unit after being reflected by the reflector 9.

[0050] The state judgment unit is used for monitoring power dynamic change and output pulse spectrum characteristics, and providing feedback basis for working state regulation and control of the pump laser unit and the pulse generation unit; the state judgment unit comprises a power meter 10 and a spectrometer 11; the power meter 10 is used for receiving the first pulse to monitor the power dynamic change of the mid-infrared wave band pulse laser; and the spectrometer 11 is used for receiving the second pulse to analyze and measure the spectrum characteristics of the mid-infrared wave band pulse laser.

[0051] A high-repetition mid-infrared waveband pulse generation method based on parametric down-conversion, the high-repetition mid-infrared waveband pulse light source based on parametric down-conversion comprises the following steps:

[0052] Step 1, generate near-infrared pump laser pulses by a near-infrared pulse laser 1, simultaneously tune the output power of a fiber amplifier 2, and then couple the near-infrared pump laser pulses into a micro-ring resonator cavity chip 4 through a lens fiber 3 after mode field compression, so that the power intensity of the near-infrared pump laser pulses meets the power threshold condition for the parametric down-conversion process of the micro-ring resonator cavity chip 4;

[0053] Figure 2 , Figure 3 The initial spectrum and time-domain waveform of the near-infrared pump laser pulses are shown in FIG. 1, the initial spectrum center wavelength is 1550 nm, the spectral width is 20 nm, and the time-domain pulse width is 1 ps; in this embodiment, the near-infrared pulse laser 1 is an active modulation type laser, the repetition frequency is 45 GHz, the peak power is only 25 W, and the average power is 1.1 W; in other embodiments, a common passive lock model laser can also be selected, but the average power of the infrared pump laser pulses after the fiber amplifier 2 must reach 1 W;

[0054] Step 2, change the working temperature and actual cavity length of the micro-ring resonator cavity chip 4 by tuning the output current or voltage of a direct current power supply 5, when the micro-ring resonator cavity chip 4 is at a suitable working temperature, the actual repetition frequency of the micro-ring resonator cavity chip 4 is an integer multiple of the near-infrared pump laser pulse repetition frequency, and several longitudinal mode frequency components of the near-infrared pump laser pulses will be converted based on the parametric down-conversion process of the second-order nonlinear χ (2) , Figure 4 as shown in FIG. 2, to realize wavelength conversion from short-wave near-infrared (i.e. 2ω0, near 1.55 μm) to long-wave mid-infrared (i.e. ω0, near 3.10 μm);

[0055] The newly generated mid-infrared waveband frequencies further expand the spectrum to both sides through the four-wave mixing process of the third-order nonlinear χ (3) , Figure 5 as shown in FIG. 3; at the same time, the generated frequency components will only occur at the micro-ring cavity resonance condition, thus having frequency equidistance and high coherence characteristics, thereby finally realizing the generation of mid-infrared waveband pulse laser;

[0056] Step 3, receive the mid-infrared waveband pulse laser output from the output port 42 of the common waveguide through a microscopic objective lens 6, filter out the residual near-infrared pump laser pulses in the mid-infrared laser pulses through a band-pass filter 7, and then divide the mid-infrared waveband pulse laser into a first pulse and a second pulse through a beam splitter 8, output the first pulse to a power meter 10 of a state judgment unit through the beam splitter 8, and output the second pulse to a spectrometer 11 of the state judgment unit through a mirror 9.

[0057] Step 4, the state judging unit monitors the power dynamic change of the mid-infrared wave band pulsed laser and the spectral characteristics of the mid-infrared wave band pulsed laser according to the first pulse and the second pulse respectively, and adjusts the pumping laser unit and the pulse generating unit according to the monitoring result until the monitoring result shows that the mid-infrared wave band pulsed laser meets the preset requirement;

[0058] Step 4.1, the power meter 10 receives the first pulse, monitors the power dynamic change of the mid-infrared wave band pulsed laser, and adjusts the output current or voltage of the direct current power supply 5 until the output current or voltage of the direct current power supply 5 is kept unchanged after the power of the mid-infrared wave band pulsed laser reaches the maximum value;

[0059] Step 4.2, the spectrometer 11 receives the second pulse, monitors the spectral characteristics of the mid-infrared wave band pulsed laser, and adjusts the output power of the fiber amplifier 2 until the output power of the fiber amplifier 2 is kept unchanged after the spectral envelope is stable and the bandwidth reaches the maximum value;

[0060] Figure 6 、 Figure 7 The spectral shape and the time domain waveform of the mid-infrared wave band pulsed laser generated by the embodiment are shown in the figure, the pulse spectral center wavelength is 3100nm, the spectral width is 610nm, the repetition frequency (i.e. the spectral longitudinal mode interval) is 51GHz, and the time domain pulse width is 0.2ps; it can be seen that, based on the parametric down-conversion process in the micro-ring resonant cavity, the mid-infrared laser pulse with low threshold, large bandwidth and high repetition frequency can be generated by near-infrared pulsed pumping.

[0061] The principle of the embodiment is that: since the cavity length of the commonly used near-infrared pulsed laser is large and the repetition frequency is low (typical value is several MHz to several tens of MHz), the longitudinal mode frequency interval is small (equal to the repetition frequency) and the comb teeth are dense; while the cavity length of the micro-ring resonant cavity is short and the repetition frequency is high (typical value is several tens to several hundreds of GHz), the longitudinal mode frequency interval is large and the comb teeth are sparse, so at least one pair of longitudinal mode components of the pumping laser pulse must exist near the resonant wavelength of the micro-ring resonant cavity chip. At the same time, since the refractive index of the micro-ring resonant cavity is different at different wave bands of near-infrared and mid-infrared, the fine tuning of the longitudinal mode frequency interval can be realized by tuning the working temperature and slightly changing the effective cavity length; when the actual repetition frequency of the micro-ring resonant cavity is an integer multiple of the repetition frequency of the near-infrared pumping laser pulse, the near-infrared pulse can be efficiently and synchronously pumped to the micro-cavity chip, so that the stable output of the mid-infrared wave band pulsed laser is realized.

[0062] The parametric down-conversion is an important frequency conversion technique in nonlinear optics, and the basic process is that a photon with high energy (pump photon) is split into a pair of photons with lower energy (down-converted photon pair) under phase matching condition after second-order nonlinearity, i.e. a photon with frequency 2ω0is converted into two photons with frequency ω0. For example, the effects of optical parametric oscillation (OPO) and optical parametric generation (OPG) all belong to the parametric down-conversion process, and compared with the third-order nonlinearity, the parametric down-conversion has low excitation threshold and high conversion efficiency, and is often used in mid-infrared or long-wave laser technology.

[0063] The above examples are only used to illustrate the technical solutions of the present application, but not to limit it. For those skilled in the art, the specific technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalent ones, and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions protected by the present application.

Claims

1. A high repetition rate mid-infrared pulsed light source based on parametric down-conversion, characterized in that: It includes a pump laser unit, a pulse generation unit, a pulse output unit, and a status determination unit, which are connected in sequence to the input and output. The pump laser unit is used to generate near-infrared pump laser pulses; The pulse generation unit includes a micro-ring resonant cavity chip (4) and a DC power supply (5); The micro-ring resonant cavity chip (4) includes a common waveguide and a micro-ring resonant cavity waveguide (43); the input port (41) of the common waveguide is connected to the output end of the lens fiber (3), and the output port (42) of the common waveguide is connected to the input end of the pulse output unit; the micro-ring resonant cavity chip (4) is used to realize the frequency conversion from near-infrared to mid-infrared band through a second-order nonlinear parametric down-conversion process, and to further broaden the spectrum through a third-order nonlinear cascaded four-wave mixing process, thereby generating mid-infrared band pulsed laser; The DC power supply (5) is used to change the operating temperature of the micro-ring resonator chip (4) and tune the actual cavity length of the micro-ring resonator chip (4); The pulse output unit is used to filter out residual near-infrared pump laser pulses in the mid-infrared band pulsed laser and to inject the mid-infrared band pulsed laser into the state determination unit after splitting the laser beam. The state determination unit is used to monitor dynamic changes in power and the spectral characteristics of the output pulse, providing feedback for the operation state control of the pump laser unit and the pulse generation unit.

2. The high repetition rate mid-infrared pulsed light source based on parametric down-conversion according to claim 1, characterized in that: The pump laser unit includes a near-infrared pulsed laser (1), an optical fiber amplifier (2), and a lens fiber (3) connected in sequence for input and output. The near-infrared pulsed laser (1) is used to generate near-infrared pump laser pulses. The optical fiber amplifier (2) is used to amplify the intensity of the near-infrared pump laser pulses. The lens fiber (3) is used to compress the mode field of the near-infrared pump laser pulses and inject them into the pulse generation unit.

3. The high repetition rate mid-infrared pulsed light source based on parametric down-conversion according to claim 2, characterized in that: The micro-ring resonant cavity chip (4) also includes a metal thermoelectric electrode (44); the positive and negative terminals of the DC power supply (5) are connected to the metal thermoelectric electrode (44).

4. The high repetition rate mid-infrared pulsed light source based on parametric down-conversion according to claim 3, characterized in that: The micro-ring resonant cavity chip (4) is made of one of lithium niobate, aluminum gallium arsenide, aluminum nitride, and gallium nitride.

5. The high repetition rate mid-infrared pulsed light source based on parametric down-conversion according to claim 3 or 4, characterized in that: The pulse output unit includes a microscope objective (6), a bandpass filter (7), a beam splitter (8), and a reflector (9) arranged sequentially along the optical path. The input end of the microscope objective (6) is connected to the output port (42) of the common waveguide. The beam splitter (8) is used to divide the mid-infrared pulsed laser into a first pulse and a second pulse. The first pulse is directly output to the state determination unit by the beam splitter (8), and the second pulse is output to the state determination unit after being reflected by the reflector (9).

6. The high repetition rate mid-infrared pulsed light source based on parametric down-conversion according to claim 5, characterized in that: The state determination unit includes a power meter (10) and a spectrometer (11); the power meter (10) is used to receive a first pulse to monitor the dynamic changes in the power of the mid-infrared pulsed laser; the spectrometer (11) is used to receive a second pulse to analyze and measure the spectral characteristics of the mid-infrared pulsed laser.

7. A method for generating high repetition rate mid-infrared band pulses based on parametric down-conversion, characterized in that, The high repetition rate mid-infrared pulsed light source based on parametric down-conversion as described in claim 1 includes the following steps: Step 1: Generate near-infrared pump laser pulses from the pump laser unit and tune the output power of the near-infrared pump laser pulses so that the intensity of the output near-infrared pump laser pulses exceeds the threshold for the pulse generation unit to undergo parametric down-conversion. Step 2: Adjust the output current or voltage of the DC power supply (5) of the pulse generation unit to change the working temperature of the micro-ring resonator chip (4), so that the micro-ring resonator chip (4) of the pulse generation unit undergoes a second-order nonlinear parametric downconversion process at this working temperature, realizes the frequency conversion from near-infrared to mid-infrared band, and realizes spectrum expansion through a third-order nonlinear cascaded four-wave mixing process to generate mid-infrared band pulsed laser. Step 3: After filtering out the residual near-infrared pump laser pulse in the mid-infrared band pulsed laser through the pulse output unit, the mid-infrared band pulsed laser is divided into a first pulse and a second pulse, which are then injected into the state determination unit respectively. Step 4: The state determination unit monitors the dynamic power change and spectral characteristics of the mid-infrared pulsed laser based on the first and second pulses, respectively. The pump laser unit and pulse generation unit are adjusted according to the monitoring results until the monitoring results show that the mid-infrared pulsed laser meets the preset requirements, thus realizing the generation of high-repetition-rate mid-infrared pulses.

8. The high repetition rate mid-infrared band pulse generation method based on parametric down-conversion according to claim 7, characterized in that, Step 1 specifically involves: Near-infrared pump laser pulses are generated by a near-infrared pulsed laser (1), and the output power of the fiber amplifier (2) is tuned so that the intensity of the output near-infrared pump laser pulses exceeds the threshold for the parametric down-conversion process of the micro-ring resonator chip (4) after amplification.

9. The high repetition rate mid-infrared band pulse generation method based on parametric down-conversion according to claim 8, characterized in that, Step 4 specifically involves: Step 4.1: Receive the first pulse through the power meter (10), monitor the dynamic change of the power of the mid-infrared pulsed laser, and adjust the output current or voltage of the DC power supply (5) until the power of the mid-infrared pulsed laser reaches the maximum value, and then keep the output current or voltage of the DC power supply (5) unchanged. Step 4.2: Receive the second pulse through the spectrometer (11), monitor the spectral characteristics of the mid-infrared pulsed laser, and adjust the output power of the fiber amplifier (2) until the spectral envelope is stable and the bandwidth reaches its maximum, and then keep the output power of the fiber amplifier (2) unchanged.

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