Frequency stabilization method and system based on acetylene molecule absorption spectrum characteristic feedback

Abstract

The invention belongs to the technical field of frequency stabilization control of a semiconductor laser, and provides a frequency stabilization method and system based on acetylene molecule absorption spectrum characteristic feedback. Closed-loop locking of laser output frequency can be realized through current and temperature combined rapid control, extraction of acetylene molecule frequency discrimination curve characteristics and construction of a mapping relation between the frequency discrimination curve characteristics and a tuning frequency stabilization center point: timely correction before frequency lock losing, frequency stabilization time prolonging and rapid back locking after frequency lock losing. The method inherits the advantages of simple device and wide application range of a traditional linear modulation absorption semiconductor DFB laser frequency stabilization system, overcomes the defect that manual correction is needed after unlocking of a traditional frequency stabilization method, and has remarkable technical advantages in application scenes where laser frequency locking is needed for a long time without human intervention.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor laser frequency stabilization control, and in particular relates to a frequency stabilization method and system based on acetylene molecule absorption spectrum characteristic feedback. Background Art

[0002] High-precision semiconductor lasers play an important role in cutting-edge scientific research, national defense and military, quantum metrology, high-end equipment manufacturing and other fields. When such lasers are applied to precision measurement systems, the stability of their frequency directly determines the measurement accuracy of the system. For semiconductor DFB lasers, it is easy for the center frequency of the laser to exceed the correction range of the servo system in long-term and industrial measurement work scenarios, resulting in loop loss of lock. With the continuous expansion of such laser field application scenarios, it is required that they have high frequency stability and reproducibility, that is, the center frequency locking point position is accurate and stable, and they are required to have unmanned automatic locking and re-locking capabilities after loss of lock.

[0003] In the prior art, commonly used semiconductor laser frequency stabilization methods can be divided into PDH (Pound-Drever-Hall) frequency stabilization technology based on FP cavity, frequency stabilization technology based on molecular / atomic gas chamber absorption peak, and frequency stabilization technology based on femtosecond optical comb, etc., according to the selected external reference. The essence of these frequency stabilization technologies is to compare the output frequency of the semiconductor laser with these high-stability frequency references in real time to obtain the frequency error signal, and then perform PI control through the servo control system to achieve frequency-stable light source output.

[0004] However, no matter which frequency stabilization method is used, due to hardware limitations, it is impossible to achieve servo control with full optical frequency coverage. This type of laser has its own drift characteristics, that is, the same control parameters but different laser output frequencies at different control times, and there is unpredictable impact noise, which will cause the frequency error signal to exceed the laser center frequency control range corresponding to the servo control range, resulting in loss of lock. The existence of the loss of lock problem has always been the key to affecting the long-term operation of this type of laser. In practical applications, manual calibration or the use of wavelength meters and other references to determine the laser center wavelength often increases the cost of obtaining a stabilized laser and limits the application range of this type of laser.

[0005] Currently, the field of semiconductor laser frequency stabilization control technology lacks a frequency stabilization method and system that is simple in device, easy to integrate, fast, and universal for semiconductor lasers that can only be tuned by temperature and current. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a frequency stabilization method and system based on acetylene molecule absorption spectrum characteristic feedback to solve the problems in the prior art. The technical solution adopted by the present invention is:

[0007] A frequency stabilization system based on the feedback of the linear absorption spectrum characteristics of acetylene molecules, comprising a tunable semiconductor laser, an optical isolator, an acetylene gas chamber, a photodetector, a digital-to-analog converter, an analog-to-digital converter, a frequency discrimination voltage output module, a TEC module, a current drive module, a single-chip microcomputer unit and an FPGA unit;

[0008] The single chip microcomputer module includes a temperature control module, a single chip microcomputer automatic locking module, a PI control module and a current control module;

[0009] The FPGA unit includes a laser modulated homologous sinusoidal signal and a frequency identification module;

[0010] The tunable semiconductor laser, the optical isolator, the acetylene gas chamber, and the photoelectric detector are connected in sequence; the photoelectric detector is connected in sequence to the analog-to-digital converter and the frequency identification module;

[0011] The laser modulates the homologous sinusoidal signal to output two sinusoidal signals, one of which is a sinusoidal signal and the output signal of the analog-to-digital converter together form the input signal of the frequency identification module, and the other sinusoidal signal is converted into an analog signal by the digital-to-analog converter and modulates the tunable semiconductor laser;

[0012] The frequency identification module is connected to the PI control module through the frequency identification voltage output module; the PI control module is connected to the single-chip microcomputer automatic locking module, and the single-chip microcomputer automatic locking module is connected to the temperature control module and the current control module; the temperature control module is connected to the tunable semiconductor laser through the TEC module; the current control module is connected to the tunable semiconductor laser through the current drive module

[0013] The digital-to-analog converter is used to convert digital quantity into analog quantity and input into the tunable semiconductor laser;

[0014] The analog-to-digital converter is used to convert the analog quantity of the photoelectric detector into a digital quantity and input it into the frequency identification module;

[0015] The frequency identification module is used to receive the digital signal from the laser modulated homologous sinusoidal signal; the frequency identification module is used to receive the acetylene linear absorption signal output by the analog-to-digital converter;

[0016] The temperature control module includes A1 and A2 programs;

[0017] The current control module includes B1, B2, B3, and B4 programs;

[0018] The single chip computer automatic locking module is used to control the temperature control module and the current control module to select a corresponding program respectively;

[0019] The temperature control module is used to adjust the TEC module, the current control module is used to control the current driving module, and the TEC module and the current driving module are used to control the laser frequency output by the tunable semiconductor laser.

[0020] A frequency stabilization method based on characteristic feedback of the linear absorption spectrum of acetylene molecules is applied to a frequency stabilization system based on characteristic feedback of the linear absorption spectrum of acetylene molecules, comprising the following steps:

[0021] In the first step, the tunable semiconductor laser is sinusoidally modulated through a digital-to-analog converter. The tunable semiconductor laser outputs laser light to the optical isolator and then enters the acetylene gas chamber. The emitted laser light enters the photodetector and is converted into an acetylene linear absorption electrical signal. After being converted by the analog-to-digital converter, the same sinusoidal signal as the laser modulation signal enters the frequency identification module of the FPGA unit for phase-locked amplification to obtain a laser frequency identification error signal.

[0022] The second step is to perform the preprocessing process of the frequency stabilization control to extract the characteristics of the frequency discrimination curve, including:

[0023] Step 2.1, the temperature control module selects the A1 terminal program: the TEC module performs a temperature scan within the range of T±T0 to obtain a complete frequency discrimination curve, T is the laser temperature lock value that is actively set, and T0 is the temperature change that can be selected according to the actual situation; the current control module selects the B2 terminal program: the output program sets the main control voltage U set Controlling the current driving module to drive the tunable semiconductor laser with a fixed current value;

[0024] Step 2.2, the temperature control module selects the A2 terminal program, and performs temperature control at a fixed temperature T through the TEC module. After the temperature control is stable; the current control module selects the B1 terminal program, and the current control voltage is U set The output range of the frequency discrimination voltage output module is U min to U max A linear scanning voltage is provided, and a current driving module is controlled to drive a tunable semiconductor laser to perform frequency scanning;

[0025] Step 2.3, from U min to U max During the linear scan process, the demodulation value of the frequency identification module is detected to see if it reaches the upper threshold value. If not, the program will jump into the lock-back procedure after the frequency stabilization is lost. If it reaches, the output value of the frequency identification module will start from the current voltage output value and move to U min Linear scan in the direction;

[0026] Step 2.4, go to U minDuring the linear scanning process in the direction, the demodulation value of the frequency identification module is detected to see if it reaches the lower threshold value Lowerthreshold. If not, it will jump into the lock-back procedure after the frequency stabilization is lost. If it reaches, it will determine the main control current drive voltage U stored in the MCU RAM according to the characteristics of the currently obtained frequency discrimination curve. set Whether the laser output frequency corresponding to the set temperature T is within the central area of ​​the servo control range corresponding to the absorption peak of the acetylene molecule to be locked; if it deviates from the central area, the frequency stabilization center deviation correction program is entered;

[0027] After the correction is completed, re-execute steps 2.1 to 2.4 to complete the locking of the tunable semiconductor laser. If it does not deviate from the center area, the pre-processing process is completed;

[0028] In the third step, the temperature control module maintains the A2 terminal program to execute the temperature control of the fixed temperature T, the current control module selects the B2 terminal program, the single chip automatic locking module receives the frequency error signal of the frequency identification module as the feedback adjustment signal of the current control module, closes the locking switch to execute the PI control of the PI control module, and locks the laser output center wavelength to the corresponding wavelength of the selected acetylene absorption peak;

[0029] The fourth step is to periodically determine whether the frequency discrimination error signal fluctuates above and below the locking point. If not, it is determined to be unlocked, and there is no need to search for peaks through steps 2.1 to 2.4 for locking. The current control module selects the triangle wave scanning program at the B3 or B4 terminal to find the voltage U corresponding to the locking point. set Store it in the MCU RAM and lock the frequency.

[0030] Furthermore, in the second step, the discrimination curve characteristics include the maximum value Curve of the discrimination electrical signal during the temperature scanning process max and minimum Curve min ; The temperature set by the master control is stably locked to T, and the initial current value is determined by the master control voltage U min The corresponding LD after the drive is stable ScanPoint ; Minimum value LD during current scanning ScanMin and maximum LD ScanMax .

[0031] Further, in step 2.4, the main control current drive voltage U stored in the MCU RAM is determined. set Whether the laser output frequency corresponding to the set temperature T is within the central area of ​​the servo control range corresponding to the absorption peak of the acetylene molecule to be locked, including:

[0032] Step 2.401, calculate abs(LD ScanPoint -Curve min )<1 / 4*(Curve max -Curvemin ) is true, if so, it is determined that the laser output frequency is within the servo control range of the acetylene molecule locking absorption peak, otherwise it is determined to be out of the servo control range and needs to be corrected;

[0033] Step 2.402, before correction, determine the correction direction and calculate the offset. If LD ScanPoint -LD ScanMin >0, then U set Need to increase, correspondingly increase the laser output wavelength; LD ScanPoint -LD ScanMin <0, then the main control current driving voltage U is reduced accordingly set ; Correction amount ΔU set =k*abs(LD ScanPoint -LD ScanMin ), where K is the proportional coefficient of the control amount.

[0034] Furthermore, in step 2.3 and step 2.4, the upper and lower thresholds selected during the current scanning process are proportional to the maximum and minimum values ​​of the frequency discrimination electrical signal.

[0035] Furthermore, in step 2.3 and step 2.4, the relocking procedure after the frequency stabilization is lost includes:

[0036] The frequency identification module controls the minimum value U within the control range of the frequency discrimination voltage output module output superimposed on the laser current control module min , determine whether the solution value of the current frequency identification module is greater than the lower threshold Lowerthreshold;

[0037] If yes, the current control module selects B4, corresponding to the main control voltage U set The triangular wave scans downward based on the current value until the demodulated value of the frequency discrimination module reaches the minimum value Curve of the frequency discrimination electrical signal during the temperature scanning process. min Then stop and set U set Store it in the MCU RAM, jump out of the lock-back program and jump into the pre-processing process;

[0038] If not, the current control module selects B3, corresponding to the main control voltage U set The triangular wave scans upward based on the current value until the demodulation value of the frequency discrimination module reaches the minimum value Curve of the frequency discrimination electrical signal during the temperature scanning process. min Then stop and set U set Store it in the MCU RAM, exit the lockback program and enter the pre-processing process.

[0039] A frequency stabilization method based on characteristic feedback of the saturated absorption spectrum of acetylene molecules, an optical coupler is arranged between the optical isolator and the acetylene gas chamber;

[0040] The laser light modulated by the digital-to-analog converter of the tunable semiconductor laser enters the optical coupler after passing through the optical isolator and is divided into two beams of light. The beam with stronger light intensity directly enters the acetylene gas chamber through a shorter optical fiber path, and the beam with weaker light intensity enters the acetylene gas chamber through a longer optical fiber path. After the two beams of light are emitted, they enter the photoelectric detector and are converted into the absorption peak signal of the gas chamber gas to eliminate the Doppler frequency shift background. After being converted by the analog-to-digital converter, the same sinusoidal signal as the laser modulation enters the frequency identification module for phase-locked amplification to extract the third harmonic to obtain the laser frequency identification error signal;

[0041] Then execute steps 2 to 4.

[0042] The present invention has the following beneficial effects:

[0043] The present invention does not need to introduce a wavelength meter and other additional photoelectric detection elements to assist in identifying the laser frequency locking state, thereby increasing the complexity of the system. Through the rapid control of current and temperature, the characteristics of the acetylene molecule frequency discrimination curve are extracted, and a mapping relationship between the characteristics of the frequency discrimination curve and the tuning and stabilization center point is constructed, so that the closed-loop locking of the laser output frequency can be achieved: timely correction before the frequency is unlocked, the stabilization time is extended, and the frequency is quickly locked back after the frequency is unlocked. The present invention inherits the advantages of the traditional linear modulation absorption semiconductor DFB laser frequency stabilization system, which is simple in device and has a wide range of applications, and overcomes the disadvantage of the traditional frequency stabilization method that manual correction is required after unlocking, and has significant technical advantages in application scenarios where long-term unmanned intervention in laser frequency locking is required. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a structural schematic diagram of a frequency stabilization system based on characteristic feedback of the linear absorption spectrum of acetylene molecules provided by the present invention;

[0045] Figure 2 It is a logic block diagram of a frequency stabilization method based on characteristic feedback of the linear absorption spectrum of acetylene molecules of the present invention;

[0046] Figure 3 It is a logic block diagram of laser frequency locking back after losing frequency lock of the present invention;

[0047] Figure 4 This is a schematic diagram of the linear absorption signal and discrimination frequency curve of acetylene molecules;

[0048] Figure 5 It is a structural schematic diagram of a frequency stabilization method based on characteristic feedback of saturated absorption spectrum of acetylene molecules provided by the present invention;

[0049] Attached: 1. Tunable semiconductor laser; 2. Optical isolator; 3. Acetylene gas chamber; 4. Photodetector; 5. Digital-to-analog converter; 6. Analog-to-digital converter; 7. Laser modulated homologous sinusoidal signal; 8. Frequency identification module; 9. Frequency discrimination voltage output module; 10. Temperature control module; 11. Single chip microcomputer automatic locking module; 12. PI control module; 13. Current control module; 14. TEC module; 15. Current drive module. DETAILED DESCRIPTION

[0050] The following will be combined with the embodiments of the present invention Figure 1-Figure 2 , the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0051] like Figure 1 , a frequency stabilization system based on the feedback of the linear absorption spectrum characteristics of acetylene molecules, comprising a tunable semiconductor laser 1, an optical isolator 2, an acetylene gas chamber 3, a photodetector 4, a digital-to-analog converter 5, an analog-to-digital converter 6, a frequency discrimination voltage output module 9, a TEC module 14, a current driving module 15, a single-chip microcomputer unit and an FPGA unit;

[0052] The single chip microcomputer module includes a temperature control module 10, a single chip microcomputer automatic locking module 11, a PI control module 12 and a current control module 13;

[0053] The FPGA unit includes a laser modulated homologous sinusoidal signal 7 and a frequency identification module 8;

[0054] The tunable semiconductor laser 1, the optical isolator 2, the acetylene gas chamber 3, and the photodetector 4 are connected in sequence; the photodetector 4 is connected in sequence to the analog-to-digital converter 6 and the frequency identification module 8;

[0055] The laser modulated homologous sinusoidal signal 7 outputs two sinusoidal signals, one of which is a sinusoidal signal and the output signal of the analog-to-digital converter 6 together form the input signal of the frequency identification module 8, and the other sinusoidal signal is converted into an analog signal by the digital-to-analog converter 5 and modulates the tunable semiconductor laser 1;

[0056] The frequency identification module 8 is connected to the PI control module 12 through the frequency identification voltage output module 9; the PI control module 12 is connected to the single-chip automatic locking module 11, and the single-chip automatic locking module 11 is connected to the temperature control module 10 and the current control module 13; the temperature control module 10 is connected to the tunable semiconductor laser 1 through the TEC module 14; the current control module 13 is connected to the tunable semiconductor laser 1 through the current driving module 15

[0057] The digital-to-analog converter 5 is used to convert the digital quantity into an analog quantity and input it into the tunable semiconductor laser 1;

[0058] The analog-to-digital converter 6 is used to convert the analog quantity of the photodetector 4 into a digital quantity and input it into the frequency identification module 8;

[0059] The frequency identification module 8 is used to receive the digital signal from the laser modulated homologous sinusoidal signal 7; the frequency identification module 8 is used to receive the acetylene linear absorption signal output by the analog-to-digital converter 6;

[0060] The temperature control module 10 includes A1 and A2 programs;

[0061] The current control module 13 includes programs B1, B2, B3, and B4;

[0062] The single chip computer automatic locking module 11 is used to control the temperature control module 10 and the current control module 13 to select a corresponding program respectively;

[0063] The temperature control module 10 is used to adjust the TEC module 14 , the current control module 13 is used to control the current driving module 15 , and the TEC module 14 and the current driving module 15 are used to control the laser frequency output by the tunable semiconductor laser 1 .

[0064] like Figure 2 , a frequency stabilization method based on the characteristic feedback of the linear absorption spectrum of acetylene molecules, comprising the following steps:

[0065] In the first step, the tunable semiconductor laser 1 is sinusoidally modulated through the digital-to-analog converter 5, and the tunable semiconductor laser 1 outputs the laser to the optical isolator 2 and then enters the acetylene gas chamber 3. The emitted laser enters the photodetector 4 and is converted into an acetylene linear absorption electrical signal. After being converted by the analog-to-digital converter 6, the laser modulation homologous sinusoidal signal 7 enters the frequency identification module 8 of the FPGA unit for phase-locked amplification to obtain a laser frequency identification error signal;

[0066] In the second step, the single-chip control platform performs the preprocessing process of frequency stabilization control to extract the characteristics of the frequency discrimination curve:

[0067] Step 2.1, the temperature control module 10 selects the A1 terminal program: the TEC module 14 performs a temperature scan within the range of T±T0 to obtain a complete discrimination curve, T is the laser temperature lock value actively set, T0 is the temperature change amount that can be selected according to the actual situation, and the selection of T0 must ensure that the temperature scanning range can obtain a complete discrimination curve, and that the acetylene absorption peak will not cross. At this time, the current control module 13 selects the B2 terminal program: the output program sets the main control voltage U set Controlling the current driving module 15 to drive the tunable semiconductor laser 1 with a fixed current value;

[0068] Step 2.2, the temperature control module 10 selects the A2 terminal program: the temperature control of the fixed temperature T is performed through the TEC module 14. After the temperature control is stable, the current control module 13 selects the B1 terminal program: the current control voltage is U set The output range of the discrimination voltage output module 9 is U min -U max Linearly scan the voltage and control the current driving module 15 to drive the tunable semiconductor laser 1 to perform frequency scanning;

[0069] Step 2.3, from U min to U max During the linear scanning process, the demodulation value of the frequency identification module 8 is detected to see if it reaches the upper threshold value Upperthreshold. If it does not reach it, the program will be jumped into the lock-back procedure after the frequency stabilization is lost. If it reaches it, the output value of the frequency identification module will start from the current voltage output value and move to U min Linear scan in the direction;

[0070] Step 2.4, go to U min During the linear scanning process in the direction, the demodulation value of the frequency identification module 8 is detected to see whether it reaches the lower threshold value Lowerthreshold. If it does not reach it, it will jump into the lock-back procedure after the frequency stabilization is lost. If it reaches it, it will judge the main control current drive voltage U stored in the single-chip computer RAM according to the characteristics of the currently obtained frequency discrimination curve. set Whether the laser output frequency corresponding to the set temperature T is in the center area of ​​the servo control range corresponding to the absorption peak of the acetylene molecule to be locked, if it deviates too much, it will enter the frequency stabilization center correction program. After the correction is completed, it is necessary to re-execute steps 2.1 to 2.4 of the preprocessing process to complete the locking of the laser 1. If the deviation of the center area is not large, the preprocessing process will be jumped out.

[0071] In the third step, after the pretreatment process is completed, the temperature control module 10 maintains the A2 terminal program to execute the temperature control of the fixed temperature T, the current control module 13 selects the B2 terminal program, the single-chip computer automatic locking module 11 receives the frequency error signal from the frequency identification module 8 in the FPGA as the feedback adjustment signal of the current control module 13, closes the locking switch to execute the PI control of the PI control module 12, and locks the laser output center wavelength to the corresponding wavelength of the selected acetylene absorption peak.

[0072] Step 4: During the long-term frequency stabilization process, the system periodically determines whether the frequency error signal fluctuates above or below the locking point or has a large floating range. If it does not fluctuate or the fluctuation increases significantly, it is determined to be unlocked. This is caused by the inherent drift of the DFB laser or the instantaneous interference of the external environment. At this time, U setThe operating point of the corresponding tunable semiconductor laser 1 is controlled to be far beyond the central area of ​​the servo control range, and there is no need to re-execute the temperature current scanning of the pre-processing process, that is, there is no need to search for peaks through steps 2.1 to 2.4 for locking. The current control module 13 selects the triangle wave scanning program at the B3 or B4 terminal to find the voltage U corresponding to the locking point. set Store it in the RAM of the microcontroller and lock the frequency directly. This design can greatly shorten the relocking time after the laser loses lock, which is more in line with the actual application requirements.

[0073] Furthermore, in the second step, the frequency discrimination curve features extracted during the preprocessing process include the maximum value Curve of the frequency discrimination electrical signal during the temperature scanning process. max and minimum Curve min ; The temperature set by the master control is stably locked to T, and the initial current value is determined by the master control voltage U min The corresponding LD after the drive is stable ScanPoint ; Minimum value LD during current scanning ScanMin and maximum LD ScanMax .

[0074] Further, in step 2.4, the main control current drive voltage U stored in the MCU RAM is determined. set Whether the laser output frequency corresponding to the set temperature T is within the central area of ​​the servo control range corresponding to the absorption peak of the acetylene molecule to be locked includes:

[0075] Step 2.401, calculate abs(LD ScanPoint -Curve min )<1 / 4*(Curve max -Curve min ) is true, 1 / 4 can be selected according to the actual situation. If so, it is determined that the laser output frequency is within the servo control range of the acetylene molecule locking absorption peak. Otherwise, it is determined to be out of the servo control range and needs to be corrected;

[0076] Step 2.402, before correction, it is necessary to determine the correction direction and calculate the offset. If LD ScanPoint -LD ScanMin >0, then U set Need to increase, correspondingly increase the laser output wavelength; LD ScanPoint -LD ScanMin <0, then reduce U set ; Correction amount ΔU set =k*abs(LD ScanPoint -LD ScanMin ), the size of k is proportional to the characteristic parameter current modulation coefficient of the tunable semiconductor laser.

[0077] Furthermore, in step 2.3 and step 2.4, the upper and lower thresholds Upperthreshold and Lowerthreshold selected during the current scanning process are the same as Curve max and Curve min The purpose is to ensure that the zero point within the current control range is located in the central linear region of the acetylene absorption discrimination frequency curve.

[0078] Further, such as Figure 3 In step 2.3 and step 2.4, the locking procedure flow after determining that the frequency stabilization is lost is as follows:

[0079] The frequency identification module 8 controls the minimum value U within the control range of the laser current control module 13 and the frequency discrimination voltage output module 9. min , determine whether the solution value of the current frequency identification module is greater than the lower threshold Lowerthreshold.

[0080] If yes, the current control module 13 selects B4, corresponding to the current control voltage U set The triangular wave scans downward based on the current value until the demodulation value of the frequency discrimination module 8 reaches the minimum value Curve of the frequency discrimination electrical signal during the temperature scanning process. min Then stop and set U set Store it in the MCU RAM, exit the lockback program and enter the pre-processing process.

[0081] If not, the current control module 13 selects B3, corresponding to the current control voltage U set The triangular wave scans upward based on the current value until the demodulation value of the frequency identification module 9 reaches the minimum value Curve of the frequency discrimination electrical signal during the temperature scanning process. min Then stop and set U set Store it in the MCU RAM, exit the lockback program and enter the pre-processing process.

[0082] A frequency stabilization method based on characteristic feedback of saturated absorption spectrum of acetylene molecules, based on the above frequency stabilization method based on characteristic feedback of linear absorption spectrum of acetylene molecules, an optical coupler is arranged between optical isolator 2 and acetylene gas chamber 3;

[0083] The laser light modulated by the tunable semiconductor laser 1 through the digital-to-analog converter 5 enters the optical coupler after passing through the optical isolator 2 and is divided into two beams of light. The beam with stronger light intensity directly enters the acetylene gas chamber 3 through the shorter optical fiber path, and the beam with weaker light intensity enters the acetylene gas chamber 3 through the longer optical fiber path. After the two beams of light are emitted, they enter the photodetector 4 and are converted into the absorption peak signal of the gas chamber gas to eliminate the Doppler frequency shift background. After being converted by the analog-to-digital converter 6, the same source sine signal as the laser modulation enters the frequency identification module 8 for phase-locked amplification to extract the third harmonic to obtain the laser frequency identification error signal;

[0084] In the present invention, the frequency stabilization method based on the characteristic feedback of the absorption spectrum of the acetylene molecule can be divided into a frequency stabilization method based on the characteristic feedback of the saturated absorption spectrum of the acetylene molecule and a frequency stabilization method based on the characteristic feedback of the linear absorption spectrum of the acetylene molecule according to the absorption state of the acetylene molecule, wherein the frequency stabilization method based on the characteristic feedback of the saturated absorption spectrum of the acetylene molecule depends on the saturated absorption state of the acetylene molecule under high light intensity, while the frequency stabilization method based on the characteristic feedback of the linear absorption spectrum of the acetylene molecule depends on the linear absorption of the acetylene molecule under low light intensity. Saturated absorption frequency stabilization usually provides higher frequency stability and is suitable for high-precision applications; while linear absorption frequency stabilization is suitable for occasions with lower requirements for frequency stability. Compared with saturated absorption, linear absorption frequency stabilization has lower requirements for optical systems. Both technologies are widely used in fields such as optical communications, spectral analysis, and lidar.

[0085] Then, the second to fourth steps, which are the same as the frequency stabilization method based on the characteristic feedback of the linear absorption spectrum of the acetylene molecule, are performed.

[0086] In addition, for the photodetector 4, in an embodiment of a frequency stabilization method based on the characteristic feedback of the saturated absorption spectrum of acetylene molecules, reference is made to Figure 5 , the photodetector 4 can be replaced by a differential detector. For the second to fourth steps, that is, the second to fourth steps of a frequency stabilization method based on the characteristic feedback of the linear absorption spectrum of acetylene molecules. The system structure based on the frequency stabilization method based on the characteristic feedback of the saturated absorption spectrum of acetylene molecules can be referred to Figure 5 , the difference is: an optical coupler is added, and the photodetector 4 is a differential detector.

[0087] The embodiments described above are only descriptions of the preferred modes of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations, modifications, and substitutions made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A frequency stabilization system based on the characteristic feedback of the linear absorption spectrum of acetylene molecules, characterized in that: It comprises a tunable semiconductor laser (1), an optical isolator (2), an acetylene gas chamber (3), a photodetector (4), a digital-to-analog converter (5), an analog-to-digital converter (6), a frequency discrimination voltage output module (9), a TEC module (14), a current driving module (15), a single-chip microcomputer unit and an FPGA unit; The single-chip computer module comprises a temperature control module (10), a single-chip computer automatic locking module (11), a PI control module (12) and a current control module (13); The FPGA unit comprises a laser modulated homologous sinusoidal signal (7) and a frequency identification module (8); A tunable semiconductor laser (1), an optical isolator (2), an acetylene gas chamber (3), and a photodetector (4) are connected in sequence; the photodetector (4) is connected in sequence to an analog-to-digital converter (6) and a frequency identification module (8); The laser modulates the homologous sinusoidal signal (7) to output two sinusoidal signals, wherein one sinusoidal signal and the output signal of the analog-to-digital converter (6) together constitute the input signal of the frequency identification module (8), and the other sinusoidal signal is converted into an analog signal by the digital-to-analog converter (5) and modulates the tunable semiconductor laser (1); The frequency identification module (8) is connected to the PI control module (12) via the frequency identification voltage output module (9); the PI control module (12) is connected to the single-chip computer automatic locking module (11), and the single-chip computer automatic locking module (11) is connected to the temperature control module (10) and the current control module (13); the temperature control module (10) is connected to the tunable semiconductor laser (1) via the TEC module (14); the current control module (13) is connected to the tunable semiconductor laser (1) via the current driving module (15). The digital-to-analog converter (5) is used to convert the digital quantity into an analog quantity and input it into the tunable semiconductor laser (1); The analog-to-digital converter (6) is used to convert the analog quantity of the photoelectric detector (4) into a digital quantity and input it into the frequency identification module (8); The frequency identification module (8) is used to receive a digital signal from a laser modulated homologous sinusoidal signal (7); the frequency identification module (8) is used to receive an acetylene linear absorption signal output by an analog-to-digital converter (6); The temperature control module (10) includes A1 and A2 programs; The current control module (13) includes programs B1, B2, B3 and B4; The single chip computer automatic locking module (11) is used to control the temperature control module (10) and the current control module (13) to respectively select a corresponding program; The temperature control module (10) is used to adjust the TEC module (14), the current control module (13) is used to control the current driving module (15), and the TEC module (14) and the current driving module (15) are used to control the laser frequency output by the tunable semiconductor laser (1).

2. A frequency stabilization method based on characteristic feedback of the linear absorption spectrum of acetylene molecules, applied to the frequency stabilization system based on characteristic feedback of the linear absorption spectrum of acetylene molecules as claimed in claim 1, characterized in that: The following steps are involved: In the first step, the tunable semiconductor laser (1) is sinusoidally modulated through a digital-to-analog converter (5), and the tunable semiconductor laser (1) outputs laser light to an optical isolator (2) and then enters an acetylene gas chamber (3). The emitted laser light enters a photodetector (4) and is converted into an acetylene linear absorption electrical signal. After being converted by an analog-to-digital converter (6), the signal enters a frequency identification module (8) of an FPGA unit with a sinusoidal signal (7) homologous to the laser modulation, and is phase-locked amplified to obtain a laser frequency identification error signal. The second step is to perform the preprocessing process of the frequency stabilization control to extract the characteristics of the frequency discrimination curve, including: Step 2.1, the temperature control module (10) selects the A1 terminal program: performs a temperature scan in the range of T±T0 through the TEC module (14) to obtain a complete frequency discrimination curve, T is the laser temperature lock value that is actively set, and T0 is the temperature change amount that can be selected according to the actual situation; the current control module (13) selects the B2 terminal program: outputs the main control voltage U set by the program set Controlling the current driving module (15) to drive the tunable semiconductor laser (1) with a fixed current value; Step 2.2, the temperature control module (10) selects the A2 terminal program, and performs temperature control at a fixed temperature T through the TEC module (14). After the temperature control is stable; the current control module (13) selects the B1 terminal program, and the current control voltage is U set The output range of the discrimination voltage output module (9) is U min toU max A linear scanning voltage is generated, and a current driving module (15) is controlled to drive a tunable semiconductor laser (1) to perform frequency scanning; Step 2.3, from U min toU max During the linear scanning process, it is detected whether the demodulated value of the frequency identification module (8) reaches the upper threshold value Upperthreshold. If it does not reach it, the program jumps into the lock-back procedure after the frequency stabilization is lost. If it reaches it, the output value of the frequency identification module (8) starts from the current voltage output value and moves to U min Linear scan in the direction; Step 2.4, go to U min During the linear scanning process in the direction, it is detected whether the demodulated value of the frequency identification module (8) reaches the lower threshold value Lowerthreshold. If it does not reach it, it jumps into the lock-back procedure after the stable frequency is lost. If it reaches it, it determines the main control current drive voltage U stored in the single chip computer RAM according to the characteristics of the currently obtained frequency discrimination curve. set Whether the laser output frequency corresponding to the set temperature T is in the center area of ​​the servo control range corresponding to the absorption peak of the acetylene molecule to be locked; if it deviates from the center area, the frequency stabilization center deviation correction program is entered; After the correction is completed, steps 2.1 to 2.4 are executed again to complete the locking of the tunable semiconductor laser (1). If the tunable semiconductor laser (1) does not deviate from the central area, the pre-processing process is completed. In the third step, the temperature control module (10) maintains the selection of the A2 terminal program to execute temperature control at a fixed temperature T, the current control module (13) selects the B2 terminal program, the single chip computer automatic locking module (11) receives the frequency error signal of the frequency identification module (8) as a feedback adjustment signal of the current control module (13), closes the locking switch to execute the PI control of the PI control module (12), and locks the laser output center wavelength to the corresponding wavelength of the selected acetylene absorption peak; The fourth step is to periodically determine whether the frequency discrimination error signal fluctuates above and below the locking point. If not, it is determined to be unlocked, and there is no need to search for peaks through steps 2.1 to 2.4 for locking. The current control module (13) selects the triangle wave scanning program at the B3 or B4 terminal to find the voltage U corresponding to the locking point. set Store it in the MCU RAM and lock the frequency.

3. A frequency stabilization method based on characteristic feedback of the linear absorption spectrum of acetylene molecules according to claim 2, characterized in that: In the second step, the discrimination curve characteristics include the maximum value Curve of the discrimination electrical signal during the temperature scanning process. max and minimum Curve min ; The temperature set by the master control is stably locked to T, and the initial current value is determined by the master control voltage U min The corresponding LD after the drive is stable ScanPoint ; Minimum value LD during current scanning ScanMin and maximum LD ScanMax .

4. A frequency stabilization method based on characteristic feedback of the linear absorption spectrum of acetylene molecules according to claim 3, characterized in that: In step 2.4, the main control current drive voltage U stored in the MCU RAM is determined. set Whether the laser output frequency corresponding to the set temperature T is within the central area of ​​the servo control range corresponding to the absorption peak of the acetylene molecule to be locked, including: Step 2.401, calculate abs(LD ScanPoint -Curve min )<1 / 4*(Curve max -Curve min ) is true, if so, it is determined that the laser output frequency is within the servo control range of the acetylene molecule locking absorption peak, otherwise it is determined to be out of the servo control range and needs to be corrected; Step 2.402, before correction, determine the correction direction and calculate the offset. If LD ScanPoint -LD ScanMin >0, then U set Need to increase, correspondingly increase the laser output wavelength; LD ScanPoint -LD ScanMin <0, then the main control current driving voltage U is reduced accordingly set ; Correction amount ΔU set =k*abs(LD ScanPoint -LD ScanMin ), where K is the proportional coefficient of the control amount.

5. The frequency stabilization method based on the characteristic feedback of the linear absorption spectrum of acetylene molecules according to claim 2 is characterized in that: In step 2.3 and step 2.4, the upper and lower thresholds selected during the current scanning process are proportional to the maximum and minimum values ​​of the frequency discrimination electrical signal.

6. The frequency stabilization method based on the characteristic feedback of the linear absorption spectrum of acetylene molecules according to claim 2 is characterized in that: In step 2.3 and step 2.4, the relocking procedure after the frequency stabilization is lost includes: The frequency identification module (8) controls the minimum value U within the control range of the frequency identification voltage output module (9) superimposed on the laser current control module (13). min , determine whether the solution value of the current frequency identification module is greater than the lower threshold Lowerthreshold; If yes, the current control module (13) selects B4, corresponding to the main control voltage U set The triangular wave scans downward based on the current value until the demodulation value of the frequency discrimination module (8) reaches the minimum value Curve of the frequency discrimination electrical signal during the temperature scanning process. min Then stop and set U set Store it in the MCU RAM, jump out of the lock-back program and jump into the pre-processing process; If not, the current control module (13) selects B3, corresponding to the main control voltage U set The triangular wave is scanned upward based on the current value until the demodulation value of the frequency discrimination module (9) reaches the minimum value Curve of the frequency discrimination electrical signal during the temperature scanning process. min Then stop and set U set Store it in the MCU RAM, exit the lockback program and enter the pre-processing process.

7. A frequency stabilization method based on characteristic feedback of saturated absorption spectrum of acetylene molecules, based on the frequency stabilization method based on characteristic feedback of linear absorption spectrum of acetylene molecules as claimed in claim 1, characterized in that: An optical coupler is provided between the optical isolator (2) and the acetylene gas chamber (3); The laser light of the tunable semiconductor laser (1) modulated by the digital-to-analog converter (5) passes through the optical isolator (2) and then enters the optical coupler to be divided into two beams of light. The beam with a stronger light intensity directly enters the acetylene gas chamber (3) through a shorter optical fiber path, and the beam with a weaker light intensity enters the acetylene gas chamber (3) through a longer optical fiber path. After the two beams of light are emitted, they enter the photoelectric detector (4) to be converted into an absorption peak signal of the gas chamber gas that eliminates the Doppler frequency shift background. After being converted by the analog-to-digital converter (6), the signals enter the frequency identification module (8) with the same source sinusoidal signal (7) of the laser modulation to perform phase-locked amplification to extract the third harmonic and obtain a laser frequency identification error signal. Then execute steps 2 to 4.

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