TDLAS light source system based on cross-frequency shift technology

Abstract

The invention discloses a TDLAS light source system based on cross-frequency shifting technology, relates to the technical field of laser frequency shifting, and solves the technical problems that when tuning the output wavelength by changing the injected current, it is difficult to steadily adjust to the expected target, resulting in repeated changes in current and thus causing frequency drift, and the bandwidth waste caused by ignoring the single use of a wide bandwidth for tuning; the invention processes laser V1 to obtain laser frequency information, and adjusts the frequency of laser V2 to near a reference frequency; obtains an error signal based on the laser frequency information and laser V2; adjusts the output frequency of laser 2 to a first frequency locking point through a feedback value obtained by processing the error signal, and synchronizes the output frequency of laser 1 to a second frequency locking point; and repeats the system cycle to cross-update the output frequencies of lasers 1 and 2; the invention can avoid the uncertainty of the output wavelength caused by repeated changes in current and thus the instability of the output frequency.

Description

Technical Field

[0001] The invention belongs to the field of optoelectronics and relates to a laser frequency shift technology, in particular to a TDLAS light source system based on a cross-frequency shift technology. Background Art

[0002] Tunable semiconductor laser absorption spectroscopy (TDLAS) is a technology that uses a tunable semiconductor laser with a narrow line width output to precisely measure the absorption spectrum of a molecule. The light source used in TDLAS technology needs to scan the entire absorption peak spectrum. Generally, the width of a single absorption peak requires a spectral scanning range of 30GHz.

[0003] Traditional light source design generally directly utilizes the current tuning characteristics of semiconductor lasers, and achieves tuning of the output wavelength by changing the injected current under the condition of controlling the laser temperature to be relatively constant. However, due to the factors of the semiconductor itself, the response of the wavelength to the current is nonlinear, and it is difficult to achieve the expected goal through a single adjustment. In addition, repeated changes in current may cause frequency drift, and frequent current adjustments will introduce slight temperature fluctuations, which will cause uncertainty in the output wavelength while consuming the life of the laser. At the same time, the single use of a wide bandwidth for tuning will lead to bandwidth waste, resulting in an increase in detection costs.

[0004] Therefore, the present invention discloses a TDLAS light source system based on cross-frequency shift technology to solve the above technical problems. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art; to this end, the present invention proposes a TDLAS light source system based on cross-frequency shifting technology, which is used to solve the technical problems that when the output wavelength is tuned by changing the injected current, it is difficult to steadily adjust to the expected target, resulting in repeated changes in the current and thus causing frequency drift, and the bandwidth waste caused by ignoring the single use of a wide bandwidth for tuning. The present invention uses the frequency of the right sideband obtained by modulating the output of a tunable laser by an electro-optical modulator as a reference frequency, locks the frequency of another laser to the reference frequency through laser feedback frequency locking technology, and uses an optical switch to synchronously lock the frequencies of the two lasers, so as to achieve cross-frequency shifting of the output light source in this way to solve the above problems.

[0006] To achieve the above object, the first aspect of the present invention provides a TDLAS light source system based on cross-frequency shift technology, comprising: a laser processing unit, and a laser sending unit and a frequency adjustment unit connected thereto;

[0007] The laser sending unit is used to send laser V1 through laser 1 and transmit the laser V1 to the laser channel to be modulated; send laser V2 through laser 2 and transmit the laser V2 to the laser channel to be frequency locked;

[0008] The laser processing unit is used to process the laser V1 to obtain laser frequency information; adjust the laser 2 so that the frequency of the laser V2 emitted by it is near the reference frequency; based on the laser frequency information obtained after processing the laser V1 and the adjusted laser V2, an error signal representing the difference between the laser V2 and the reference frequency is obtained; wherein the laser frequency information includes the carrier frequency and the reference frequency; the vicinity of the reference frequency refers to the frequency interval [f0+fm-fk, f0+fm+fk], and fk can be manually set according to actual conditions;

[0009] The frequency adjustment unit is used to process the error signal to obtain a feedback value for adjusting the laser injection current, adjust the output frequency of laser 2 to a first frequency locking point through the feedback value, and mark the step as step one; synchronize the output frequency of laser 1 to a second frequency locking point, and mark the step as step two; summarize step one and step two into a system cycle; repeat the system cycle to cross-update the output frequencies of lasers 1 and 2; wherein the first frequency locking point is the reference frequency in step one, and the second frequency locking point is the reference frequency in step two.

[0010] It is worth noting that in the traditional method, directly changing the laser frequency in one step requires a bandwidth of tens of GHz, while the present invention uses cross-frequency shifting technology to gradually move the frequencies of the two lasers in a small bandwidth range. It only needs to repeat this process to meet the requirements of the laser frequency. In addition, the present invention only moves a small bandwidth at a time, which can reduce the bandwidth requirements for the RF source, modulator and related supporting equipment.

[0011] Preferably, the processing of the laser V1 to obtain laser frequency information includes:

[0012] A modulation signal is added to the electro-optic modulator of the laser processing unit, and the laser V1 is sent to the electro-optic modulator, and the carrier frequency f0 containing the laser V1, the sum and difference frequencies of the carrier frequency f0 and the modulation frequency fm are obtained under the birefringence of the electro-optic modulator; wherein the modulation frequency fm is the frequency of the modulation signal added to the electro-optic modulator, and the value n is nGHz, and the value n is obtained by manual setting; the sum and difference frequencies include f0+fm and f0-fm;

[0013] Mark f0+fm in the sum and difference frequencies as the reference frequency of the step being performed in this cycle.

[0014] It should be noted that the reference frequency in this system cycle is obtained by adding nGHz to the carrier frequency f0 of the laser V1. Each time the system goes through a system cycle, the carrier frequency f0 of the laser V1 will be synchronized to the reference frequency used in this system cycle. Therefore, it can be understood that the value of the carrier frequency f0 of the laser V1 will increase by nGHz after a system cycle.

[0015] Preferably, the step of adjusting the laser 2 so that the frequency of the laser V2 emitted by the laser 2 is near the reference frequency comprises:

[0016] A1: Get the laser V2 frequency emitted by laser 2 by adjusting the injection current of laser 2; determine whether the laser V2 frequency is near the reference frequency; if yes, stop current adjustment; if no, jump to A2;

[0017] A2: Determine whether the frequency of the laser V2 is greater than the maximum value of the range near the reference frequency; if yes, reduce the current and jump to A1; if no, increase the current and jump to A1; wherein the maximum value of the range is f0+fm+fk.

[0018] Preferably, the error signal representing the difference between the laser V2 and the reference frequency obtained based on the laser frequency information obtained after processing the laser V1 and the adjusted laser V2 includes:

[0019] The processed laser V1 and the adjusted laser V2 are coupled through a 2×2 optical fiber coupling module in the laser processing unit, and the coupled laser is transmitted to a high-speed photodetector in the laser processing unit for frequency mixing to obtain an output signal; wherein the laser before coupling includes four frequencies, namely, the frequency difference between the carrier frequency and the modulation frequency, the adjusted laser V2 frequency, and the carrier frequency and reference frequency of the laser V1;

[0020] The output signal of the photodetector is passed through a low-pass or band-pass filter to obtain an error signal representing the difference between the laser V2 and the reference frequency.

[0021] Preferably, the step of processing the error signal to obtain a feedback value for adjusting the laser injection current includes:

[0022] The error signal is transmitted to the PID feedback controller of the frequency adjustment unit through a cable, and the most recently transmitted error signal e(t) is obtained. The current error is processed based on the formula DFZ=Kp×e(t) to obtain the current error feedback value DFZ;

[0023] Based on the formula JFZ=Ki×∫e(t)dt, the error accumulation is processed to obtain the error accumulation feedback value JFZ;

[0024] The rate of change of the error signal is processed based on the formula WFZ=Kd×de(t) / dt to obtain the rate of change feedback value WFZ; wherein Kp is the proportional gain coefficient, Ki is the integral gain coefficient, and Kd is the differential gain coefficient;

[0025] Based on the formula FZ=DFZ+JFZ+WFZ, the feedback value FZ for adjusting the laser injection current is obtained.

[0026] It should be noted that the formula DFZ=Kp×e(t) is mainly responsible for quickly responding to frequency deviations; the formula JFZ=Ki×∫e(t)dt processes the accumulated amount of the error signal over time, and is mainly used to eliminate steady-state errors; WFZ=Kd×de(t) / dt processes the rate of change of the error signal, and is mainly used to predict future errors and respond quickly to reduce oscillations.

[0027] Preferably, adjusting the output frequency of the laser 2 to the first frequency locking point by means of the feedback value comprises:

[0028] A feedback value FZ for adjusting the laser injection current is extracted, and the feedback value FZ is transmitted to the current tuning end of the laser 2 to change the output frequency of the laser 2 to the first frequency locking point.

[0029] Preferably, synchronizing the output frequency of the laser 1 to the second frequency locking point includes:

[0030] Switch the optical path through the optical switch module, transmit the laser V2 to the laser channel to be modulated, and transmit the laser V1 to the laser channel to be frequency-locked; process the laser V2 to obtain laser frequency information; adjust the laser 1 so that the frequency of the laser V1 emitted by it is near the reference frequency; based on the laser frequency information obtained after processing the laser V2 and the adjusted laser V1, obtain an error signal representing the difference between the laser V1 and the reference frequency;

[0031] The error signal is processed to obtain a feedback value for adjusting the laser injection current, and the output frequency of the laser 1 is adjusted to the second locking frequency point through the feedback value.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The present invention uses the frequency of the right sideband obtained by modulating the output of a tunable laser through an electro-optical modulator as a reference frequency, locks the frequency of another laser to the reference frequency through laser feedback frequency locking technology, and uses an optical switch to synchronously lock the frequencies of the two lasers, so as to achieve cross-frequency shifting of the output light source, thereby solving the technical problems of repeated changes in current caused by the difficulty in steadily adjusting the output wavelength to the expected target and thus causing frequency drift, and ignoring the waste of bandwidth caused by tuning in a single wide bandwidth; the present invention can avoid the uncertainty of the output wavelength caused by repeated changes in current and thus the instability of the output frequency, while reducing the bandwidth requirements for the radio frequency source, modulator and related supporting equipment.

[0034] 2. The present invention obtains a feedback value by transmitting an error signal representing the difference between the laser V2 and the reference frequency to a PID feedback controller, and uses this feedback value as a dynamic adjustment signal of the laser current to change the output frequency of the laser 2 in real time, so that the output frequency of the laser 2 is stabilized at a frequency position nGHz higher than the output frequency of the laser 1, and then uses an optical switch to synchronize the frequency of the laser 1 to a frequency position nGHz higher than the output frequency of the laser 2 to achieve cross-frequency shifting; then repeat the above steps to gradually increase the output frequency of the laser 2 by 2nGHz, which can be used to achieve discrete point measurement of the spectrum, such as chopping, amplifying and outputting to the measured scene, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 It is a schematic diagram of the operation steps of the present invention;

[0037] Figure 2 It is a schematic diagram of the system module of the present invention;

[0038] Figure 3 This is a principle connection diagram of step one of the present invention;

[0039] Figure 4 This is the principle connection diagram of step 2 of the present invention;

[0040] Figure 5 This is a schematic diagram of the modulated laser frequency obtained in the present invention. DETAILED DESCRIPTION

[0041] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] See also Figure 1-Figure 5 , the first aspect of the present invention provides a TDLAS light source system based on cross-frequency shift technology, including: a laser processing unit, and a laser sending unit and a frequency adjustment unit connected thereto;

[0043] Laser sending unit: used to send laser V1 through laser 1, and transmit laser V1 to the laser channel to be modulated; send laser V2 through laser 2, and transmit laser V2 to the laser channel to be frequency locked;

[0044] Laser processing unit: used to process laser V1 to obtain laser frequency information; adjust laser 2 so that the frequency of laser V2 emitted by it is near the reference frequency; obtain an error signal representing the difference between laser V2 and the reference frequency based on the laser frequency information obtained after processing laser V1 and the adjusted laser V2; wherein the laser frequency information includes the carrier frequency and the reference frequency; the vicinity of the reference frequency refers to the frequency interval [f0+fm-fk, f0+fm+fk], and fk can be manually set according to the actual situation;

[0045] Frequency adjustment unit: used for processing the error signal to obtain a feedback value for adjusting the laser injection current, adjusting the output frequency of laser 2 to a first frequency locking point through the feedback value, and marking the step as step one; synchronizing the output frequency of laser 1 to a second frequency locking point, and marking the step as step two; summarizing step one and step two into a system loop; repeating the system loop to cross-update the output frequencies of lasers 1 and 2; wherein the first frequency locking point is the reference frequency in step one, and the second frequency locking point is the reference frequency in step two.

[0046] It should be noted that step 2 is to use an optical switch to switch the optical path, swap the channels entered by lasers V1 and V2 in step 1, and then repeat the operation once to adjust the output of the locked laser 1 so that the frequency of laser V1 increases by nGHz based on laser V2.

[0047] It should be noted that the laser 1 and the laser 2 are tunable distributed feedback lasers.

[0048] For example, in this embodiment, the modulation frequency fm of the modulation signal is 1 GHz, the carrier frequency f0 of the laser V1 emitted by the laser 1 before the first frequency shift is 1.935×10^5 GHz, and the value of fk is 0.1 GHz; therefore, the frequency interval near the reference frequency [f0+fm-fk, f0+fm+fk] is specifically:

[0049] [1.935×10^5GHz+0.9GHz,1.935×10^5GHz+1.1GHz];

[0050] A modulation signal is added to the electro-optic modulator of the laser processing unit, and the laser V1 is sent to the electro-optic modulator. Under the birefringence of the electro-optic modulator, the carrier frequency f0=1.935×10^5GHz containing the laser V1 is obtained. The sum and difference frequencies of the carrier frequency f0 and the modulation frequency fm are:

[0051] f0+fm=1.935×10^5GHz+1GHz, f0-fm=1.935×10^5GHz-1GHz;

[0052] Mark f0+fm=1.935×10^5GHz+1GHz as the reference frequency of the current step in this cycle;

[0053] In this embodiment, the frequency of the laser V2 emitted by the laser 2 is obtained by adjusting the injection current of the laser 2: 1.935×10^5GHz+0.8GHz. Since 1.935×10^5GHz+0.8GHz is not near the reference frequency and is not greater than the maximum value of the range near the reference frequency, 1.935×10^5GHz+1.1GHz, the frequency of the laser V2 emitted by the laser 2 is obtained by increasing the current: 1.935×10^5GHz+0.95GHz.

[0054] Since 1.935×10^5GHz+0.95GHz is near the reference frequency, current regulation is stopped;

[0055] The processed laser V1 and the adjusted laser V2 are coupled through a 2×2 optical fiber coupling module in the laser processing unit, and the coupled laser is transmitted to a high-speed photodetector in the laser processing unit for frequency mixing to obtain an output signal; the output signal of the photodetector is passed through a low-pass or band-pass filter to obtain an error signal representing the difference between the laser V2 and the reference frequency;

[0056] The error signal is transmitted to the PID feedback controller of the frequency adjustment unit through a cable, and the most recently transmitted error signal e(t) is obtained. The current error is processed based on the formula DFZ=Kp×e(t) to obtain the current error feedback value DFZ;

[0057] Based on the formula JFZ=Ki×∫e(t)dt, the error accumulation is processed to obtain the error accumulation feedback value JFZ;

[0058] The rate of change of the error signal is processed based on the formula WFZ=Kd×de(t) / dt to obtain the rate of change feedback value WFZ; wherein Kp is the proportional gain coefficient, Ki is the integral gain coefficient, and Kd is the differential gain coefficient;

[0059] Based on the formula FZ=DFZ+JFZ+WFZ, the feedback value FZ for adjusting the laser injection current is obtained;

[0060] Extracting a feedback value FZ for adjusting the laser injection current, and transmitting the feedback value FZ to the current tuning end of the laser 2 to change the output frequency of the laser 2 to a first locking frequency point;

[0061] Switch the optical path through the optical switch module, transmit the laser V2 to the laser channel to be modulated, and transmit the laser V1 to the laser channel to be frequency-locked; process the laser V2 to obtain laser frequency information; adjust the laser 1 so that the frequency of the laser V1 emitted by it is near the reference frequency; based on the laser frequency information obtained after processing the laser V2 and the adjusted laser V1, obtain an error signal representing the difference between the laser V1 and the reference frequency;

[0062] The error signal is processed to obtain a feedback value for adjusting the laser injection current, and the output frequency of the laser 1 is adjusted to the second locking frequency point through the feedback value.

[0063] In this application, the laser V1 is processed to obtain laser frequency information, including:

[0064] A modulation signal is added to the electro-optic modulator of the laser processing unit, and the laser V1 is sent to the electro-optic modulator. Under the birefringence of the electro-optic modulator, the carrier frequency f0 containing the laser V1, the sum and difference frequencies of the carrier frequency f0 and the modulation frequency fm are obtained; wherein the modulation frequency fm is the frequency of the modulation signal added to the electro-optic modulator, and the value n is nGHz, and the value n is obtained by manual setting; the sum and difference frequencies include f0+fm and f0-fm;

[0065] Mark f0+fm in the sum and difference frequencies as the reference frequency of the step being performed in this cycle.

[0066] In the present application, adjusting the laser 2 so that the frequency of the laser V2 emitted by it is near the reference frequency includes:

[0067] A1: Get the laser V2 frequency emitted by laser 2 by adjusting the injection current of laser 2; determine whether the laser V2 frequency is near the reference frequency; if yes, stop current adjustment; if no, jump to A2;

[0068] A2: Determine whether the frequency of the laser V2 is greater than the maximum value of the range near the reference frequency; if yes, reduce the current and jump to A1; if no, increase the current and jump to A1; wherein the maximum value of the range is f0+fm+fk.

[0069] It should be noted that the light source design can utilize the current tuning characteristics of semiconductor lasers to adjust the output frequency by changing the injected current while controlling the laser temperature to be relatively constant. For distributed feedback lasers, an increase in current will lead to an increase in frequency, and a decrease in current will lead to a decrease in frequency.

[0070] In the present application, based on the laser frequency information obtained after processing the laser V1 and the adjusted laser V2, an error signal representing the difference between the laser V2 and the reference frequency is obtained, including:

[0071] The processed laser V1 and the adjusted laser V2 are coupled through a 2×2 optical fiber coupling module in the laser processing unit, and the coupled laser is transmitted to a high-speed photodetector in the laser processing unit for frequency mixing to obtain an output signal; wherein the laser before coupling includes four frequencies, namely, the frequency difference between the carrier frequency and the modulation frequency, the adjusted laser V2 frequency, and the carrier frequency and reference frequency of the laser V1;

[0072] The output signal of the photodetector is passed through a low-pass or band-pass filter to obtain an error signal representing the difference between the laser V2 and the reference frequency.

[0073] It should be noted that the error signal representing the difference between the laser V2 and the reference frequency is specifically explained as: a signal representing the difference between the laser V2 and the reference frequency obtained after filtering.

[0074] In the present application, the error signal is processed to obtain a feedback value for adjusting the laser injection current, including:

[0075] The error signal is transmitted to the PID feedback controller of the frequency adjustment unit through a cable, and the most recently transmitted error signal e(t) is obtained. The current error is processed based on the formula DFZ=Kp×e(t) to obtain the current error feedback value DFZ;

[0076] Based on the formula JFZ=Ki×∫e(t)dt, the error accumulation is processed to obtain the error accumulation feedback value JFZ;

[0077] The rate of change of the error signal is processed based on the formula WFZ=Kd×de(t) / dt to obtain the rate of change feedback value WFZ; wherein Kp is the proportional gain coefficient, Ki is the integral gain coefficient, and Kd is the differential gain coefficient;

[0078] Based on the formula FZ=DFZ+JFZ+WFZ, the feedback value FZ for adjusting the laser injection current is obtained.

[0079] In the present application, the output frequency of the laser 2 is adjusted to the first frequency locking point by the feedback value, including:

[0080] A feedback value FZ for adjusting the laser injection current is extracted, and the feedback value FZ is transmitted to the current tuning end of the laser 2 to change the output frequency of the laser 2 to the first frequency locking point.

[0081] In the present application, synchronizing the output frequency of the laser 1 to the second frequency locking point includes:

[0082] Switch the optical path through the optical switch module, transmit the laser V2 to the laser channel to be modulated, and transmit the laser V1 to the laser channel to be frequency-locked; process the laser V2 to obtain laser frequency information; adjust the laser 1 so that the frequency of the laser V1 emitted by it is near the reference frequency; based on the laser frequency information obtained after processing the laser V2 and the adjusted laser V1, obtain an error signal representing the difference between the laser V1 and the reference frequency;

[0083] The error signal is processed to obtain a feedback value for adjusting the laser injection current, and the output frequency of the laser 1 is adjusted to the second locking frequency point through the feedback value.

[0084] Some of the data in the above formula are calculated by removing the dimension and taking the numerical value thereof. The preset parameters and preset thresholds in the formula are set by technicians in this field according to actual conditions.

[0085] Working principle of the present invention:

[0086] The present invention processes laser V1 to obtain laser frequency information, and adjusts laser 2 so that the frequency of laser V2 emitted by it is located near a reference frequency; based on the laser frequency information obtained after processing laser V1 and the adjusted laser V2, an error signal representing the difference between laser V2 and the reference frequency is obtained, the error signal is transmitted to a PID feedback controller to obtain a feedback value, and the feedback value is used as a dynamic adjustment signal of the laser current to change the output frequency of laser 2 in real time, so that the output frequency of laser 2 is stabilized at a frequency position nGHz higher than the output frequency of laser 1, and then an optical switch is used to synchronize the frequency of laser 1 to a frequency position nGHz higher than the output frequency of laser 2, so as to realize cross-frequency shifting.

[0087] The above embodiments are only used to illustrate the technical method of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical method of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical method of the present invention.

Claims

1. The TDLAS light source system based on cross-frequency shift technology is characterized by: include: A laser processing unit, and a laser sending unit and a frequency adjustment unit connected thereto; The laser sending unit is used to send laser V1 through laser 1 and transmit the laser V1 to the laser channel to be modulated; send laser V2 through laser 2 and transmit the laser V2 to the laser channel to be frequency locked; The laser processing unit is used to process the laser V1 to obtain laser frequency information; adjust the laser 2 so that the frequency of the laser V2 emitted by it is near the reference frequency; based on the laser frequency information obtained after processing the laser V1 and the adjusted laser V2, an error signal representing the difference between the laser V2 and the reference frequency is obtained; wherein the laser frequency information includes the carrier frequency and the reference frequency; the vicinity of the reference frequency refers to the frequency interval [f0+fm-fk, f0+fm+fk], f0 is the carrier frequency, fm is the modulation frequency, and fk is manually set according to actual conditions; The frequency adjustment unit is used to process the error signal to obtain a feedback value for adjusting the laser injection current, and adjust the output frequency of the laser 2 to the first frequency locking point through the feedback value; and mark step 1 and step 2; The step 1 comprises: emitting laser V1 through laser 1, and transmitting laser V1 to a laser channel to be modulated; emitting laser V2 through laser 2, and transmitting laser V2 to a laser channel to be frequency-locked; processing laser V1 to obtain laser frequency information; adjusting laser 2 so that the frequency of laser V2 emitted by it is near a reference frequency; obtaining an error signal representing the difference between laser V2 and the reference frequency based on the laser frequency information obtained after processing laser V1 and the adjusted laser V2; processing the error signal to obtain a feedback value for adjusting the laser injection current, and adjusting the output frequency of laser 2 to a first frequency-locking point through the feedback value; The step 2 comprises: synchronizing the output frequency of the laser 1 to a second frequency locking point; Summarize step 1 and step 2 into a system cycle; repeat the system cycle to cross-update the output frequencies of laser 1 and laser 2; wherein the first frequency locking point is the reference frequency in step 1, and the second frequency locking point is the reference frequency in step 2; The step of synchronizing the output frequency of the laser 1 to the second frequency locking point includes: Switch the optical path through the optical switch module, transmit the laser V2 to the laser channel to be modulated, and transmit the laser V1 to the laser channel to be frequency-locked; process the laser V2 to obtain laser frequency information; adjust the laser 1 so that the frequency of the laser V1 emitted by it is near the reference frequency; based on the laser frequency information obtained after processing the laser V2 and the adjusted laser V1, obtain an error signal representing the difference between the laser V1 and the reference frequency; The error signal is processed to obtain a feedback value for adjusting the laser injection current, and the output frequency of the laser 1 is adjusted to the second locking frequency point through the feedback value.

2. The TDLAS light source system based on cross-frequency shift technology according to claim 1, characterized in that: The processing of the laser V1 to obtain laser frequency information includes: A modulation signal is added to the electro-optic modulator of the laser processing unit, and the laser V1 is sent to the electro-optic modulator, and the carrier frequency f0 containing the laser V1, the sum and difference frequencies of the carrier frequency f0 and the modulation frequency fm are obtained under the birefringence of the electro-optic modulator; wherein the modulation frequency fm is the frequency of the modulation signal added to the electro-optic modulator, and the value is nGHz; the sum and difference frequencies include f0+fm and f0-fm; Mark f0+fm in the sum and difference frequencies as the reference frequency of the step being performed in this cycle.

3. The TDLAS light source system based on cross-frequency shift technology according to claim 1, characterized in that: The step of adjusting the laser 2 so that the frequency of the laser V2 emitted by the laser 2 is near the reference frequency comprises: A1: Get the laser V2 frequency emitted by laser 2 by adjusting the injection current of laser 2; determine whether the laser V2 frequency is near the reference frequency; if yes, stop current adjustment; if no, jump to A2; A2: Determine whether the frequency of the laser V2 is greater than the maximum value of the range near the reference frequency; if yes, reduce the current and jump to A1; if no, increase the current and jump to A1; wherein the maximum value of the range is f0+fm+fk.

4. The TDLAS light source system based on cross-frequency shift technology according to claim 1, characterized in that: The error signal representing the difference between the laser V2 and the reference frequency is obtained based on the laser frequency information obtained after processing the laser V1 and the adjusted laser V2, including: The processed laser V1 and the regulated laser V2 are coupled through a 2×2 fiber coupling module in the laser processing unit, and the coupled laser is transmitted to a high-speed photodetector in the laser processing unit for frequency mixing to obtain an output signal; The output signal of the photodetector is passed through a low-pass or band-pass filter to obtain an error signal representing the difference between the laser V2 and the reference frequency.

5. The TDLAS light source system based on cross-frequency shift technology according to claim 4, characterized in that: The step of processing the error signal to obtain a feedback value for adjusting the laser injection current includes: The error signal is transmitted to the PID feedback controller of the frequency adjustment unit through a cable, and the most recently transmitted error signal e(t) is obtained. The current error is processed based on the formula DFZ=Kp×e(t) to obtain the current error feedback value DFZ; Based on the formula JFZ=Ki×∫e(t)dt, the error accumulation is processed to obtain the error accumulation feedback value JFZ; The rate of change of the error signal is processed based on the formula WFZ=Kd×de(t) / dt to obtain the rate of change feedback value WFZ; wherein Kp is the proportional gain coefficient, Ki is the integral gain coefficient, and Kd is the differential gain coefficient; Based on the formula FZ=DFZ+JFZ+WFZ, the feedback value FZ for adjusting the laser injection current is obtained.

6. The TDLAS light source system based on cross-frequency shift technology according to claim 5, characterized in that: The step of adjusting the output frequency of the laser 2 to the first frequency locking point by means of the feedback value comprises: A feedback value FZ for adjusting the laser injection current is extracted, and the feedback value FZ is transmitted to the current tuning end of the laser 2 to change the output frequency of the laser 2 to the first frequency locking point.

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