A frequency stabilizing method and system based on feedback of spectral characteristics of acetylene molecule absorption

Abstract

The present application belongs to the technical field of frequency stabilization control of semiconductor laser, and provides a frequency stabilization method and system based on acetylene molecular absorption spectrum characteristics feedback, which can realize closed-loop locking of laser output frequency by current-temperature joint fast control, extraction of acetylene molecular frequency discrimination curve characteristics, construction of the mapping relationship between the frequency discrimination curve characteristics and the tuning frequency stabilization center point, timely correction before frequency unlocking, extension of frequency stabilization time and fast relocking after frequency unlocking, without the need to introduce a wavemeter and other additional optoelectronic detection elements to assist in discriminating the laser frequency locking state, thereby increasing the complexity of the system, inheriting the advantages of simple device and wide application range of the traditional linear modulation absorption semiconductor DFB laser frequency stabilization system, overcoming the shortcomings of manual correction after unlocking of the traditional frequency stabilization method, and having significant technical advantages in long-term unattended application scenarios requiring laser frequency locking.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of frequency stabilization control of semiconductor lasers, and particularly relates to a frequency stabilization method and system based on acetylene molecular absorption spectrum characteristic feedback. BACKGROUND

[0002] High-precision semiconductor lasers play an important role in the fields of frontier scientific research, national defense and military, quantum metrology, high-end equipment manufacturing, etc. When such lasers are applied to precision measurement systems, the stability of the frequency of the lasers directly determines the measurement accuracy of the systems. For semiconductor DFB lasers in long-time and industrial measurement working scenarios, the center frequency of the lasers can easily exceed the correction range of the servo system, resulting in loop lock loss. With the continuous expansion of the application scenarios of such lasers, it is required that the lasers have high frequency stability and repeatability, i.e., the center frequency lock point position is accurate and stable, and the lasers also need to have the ability of automatic locking and re-locking after lock loss.

[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 F-P 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 a frequency error signal, and then perform PI control through a servo control system to realize the output of a frequency-stable light source.

[0004] However, regardless of which frequency stabilization method is used, due to hardware limitations, it is impossible to realize full optical frequency coverage servo control. Such lasers have their own drift characteristics, i.e., the laser output frequency is different at different control times under the same control parameters, and there are unpredictable impact noises, which will all cause the frequency error signal to exceed the corresponding laser center frequency control range of the servo control range, resulting in lock loss. The existence of the lock loss problem has always been a key factor affecting the long-term work of such lasers. In actual applications, manual correction or reference to a wavelength meter is often needed to determine the laser center wavelength, which increases the cost of obtaining a frequency-stabilized laser and also limits the application range of such lasers.

[0005] At present, there is a lack of a frequency stabilization method and system that is simple in device, easy to integrate, fast, and has universality for semiconductor lasers that are only temperature and current tuned in the technical field of frequency stabilization control of semiconductor lasers. SUMMARY

[0006] To solve the above technical problems, the application provides a frequency stabilization method and system based on acetylene molecular absorption spectrum characteristic feedback to solve the problems in the prior art. The technical solution adopted by the application is as follows:

[0007] A frequency stabilization system based on feedback of the linear absorption spectrum characteristics of acetylene molecules includes 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, together with the output signal of the analog-to-digital converter, constitutes 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 discrimination 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 quantities into analog quantities and input them into tunable semiconductor lasers;

[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 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 an optical isolator and then enters the acetylene gas chamber. The emitted laser light enters a photodetector and is converted into an acetylene linear absorption electrical signal. After conversion 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 preprocessing 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 actively set laser temperature lock value, 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 As the center, the output range of the frequency discrimination voltage output module is U min toU max The linear scanning voltage is controlled to drive the tunable semiconductor laser to perform frequency scanning;

[0025] Step 2.3, from U min toU 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 value, 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 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 correction program is entered;

[0027] After the correction is completed, repeat 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 selection of the A2 terminal program to execute temperature control at a fixed temperature T, the current control module selects the B2 terminal program, the single-chip microcomputer 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 wavelength corresponding to the selected acetylene absorption peak;

[0029] The fourth step is to periodically determine whether the frequency 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 to lock. 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 frequency discrimination curve characteristics 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 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] Furthermore, 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 center 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 corresponding main control current driving voltage U is reduced 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 steps 2.3 and 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 so, the current control module selects B4, corresponding to the main control voltage U set The triangle wave scans downward based on the current value until the demodulated value of the frequency identification 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 jump into the pre-processing process;

[0038] If not, the current control module selects B3, corresponding to the main control voltage U set The triangle wave is scanned upward based on the current value until the demodulated value of the frequency identification 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 jump into the pre-processing process.

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

[0040] After being modulated by a digital-to-analog converter, the tunable semiconductor laser passes through an optical isolator and then enters an optical coupler to be split into two beams. The stronger beam directly enters the acetylene gas chamber through a shorter optical fiber path, while the weaker beam enters the acetylene gas chamber through a longer optical fiber path. After being emitted, the two beams enter a photodetector and are converted into absorption peak signals of the gas chamber gas to eliminate the Doppler frequency shift background. After being converted by an 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 and obtain a laser frequency identification error signal.

[0041] Then execute steps 2 to 4.

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

[0043] Without the need for a wavelength meter or other additional photoelectric detection elements to aid in identifying the laser frequency lock state, which would increase system complexity, this invention rapidly combines current and temperature control to extract the characteristics of the acetylene molecular frequency discrimination curve. This mapping relationship between the discrimination curve characteristics and the tuning and stabilization center point is then established, enabling closed-loop locking of the laser output frequency. This allows for timely correction before frequency loss, extended frequency stabilization time, and rapid relock after frequency loss. This invention inherits the advantages of traditional linearly modulated absorption semiconductor DFB laser frequency stabilization systems, which offer simplicity and a wide range of applications. It overcomes the drawback of traditional frequency stabilization methods, which require manual correction after loss of frequency. This presents significant technical advantages in applications requiring long-term, unattended laser frequency locking. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

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

[0049] Appendix: 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. Microcontroller automatic locking module; 12. PI control module; 13. Current control module; 14. TEC module; 15. Current drive module. DETAILED DESCRIPTION

[0050] The following is a combination of 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 includes 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, together with the output signal of the analog-to-digital converter 6, constitutes 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 discrimination 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 drive 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 value of the photoelectric detector 4 into a digital value 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 programs A1 and A2;

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

[0062] The single chip 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 feedback of the linear absorption spectrum characteristics of acetylene molecules comprises the following steps:

[0065] In the first step, the tunable semiconductor laser 1 is sinusoidally modulated through the digital-to-analog converter 5. The tunable semiconductor laser 1 outputs laser light to the optical isolator 2 and then enters the acetylene gas chamber 3. The emitted laser light enters the photodetector 4 and is converted into an acetylene linear absorption electrical signal. After conversion 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 preprocessing of the 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: executes the temperature scan within the range of T±T0 through the TEC module 14 to obtain a complete frequency discrimination curve, T is the actively set laser temperature lock value, 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 the complete frequency discrimination curve and that the acetylene absorption peak will not be crossed. At this time, 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;

[0068] Step 2.2, the temperature control module 10 selects the A2 terminal program: the temperature control of the fixed temperature T is performed by 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 As the center, the output range of the frequency 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 toU max During the linear scan process, the demodulation value of the frequency identification module 8 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 value, 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 if 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 determine the main control current drive voltage U stored in the single chip RAM according to the characteristics of the currently obtained frequency discrimination curve. set Is the laser output frequency corresponding to the set temperature T within 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, the frequency stabilization center correction program will be entered. After the correction is completed, steps 2.1 to 2.4 of the preprocessing process need to be re-executed to complete the locking of the laser 1. If the deviation of the center area is not large, the preprocessing process will be exited.

[0071] In the third step, after the pretreatment process is completed, the temperature control module 10 maintains the selection of the A2 end program to execute temperature control with a fixed temperature T, the current control module 13 selects the B2 end program, and 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] The fourth step is to periodically judge whether the frequency error signal fluctuates above and below the locking point or the floating range is large during the long-term frequency stabilization process of the system. If it does not fluctuate or the fluctuation increases significantly, it is judged as unlocked. This situation is caused by the inherent drift of the DFB laser or the instantaneous interference of the external environment. At this time, U setThe working point of the corresponding tunable semiconductor laser 1 does not go beyond the center region of the servo control range, and the temperature current scanning of the pre-processing process does not need to be re-executed, that is, the locking is not needed by peak searching through steps 2.1-2.4, the current control module 13 selects the B3 or B4 end triangular wave scanning program to find the voltage U corresponding to the locking point set The frequency locking is directly performed by storing in the single-chip microcomputer RAM, which can greatly shorten the relocking time of the laser after losing lock and is more in line with the actual application requirements.

[0073] Further, in the second step, the frequency discrimination curve features extracted in the pre-processing process include the maximum value Curve max and the minimum value Curve min of the frequency discrimination electric signal in the temperature scanning process; the temperature set by the main control is locked to T, and the initial value of the current is the LD min corresponding to the main control voltage U ScanPoint driven and stabilized; the minimum value LD ScanMin and the maximum value LD ScanMax in the current scanning process.

[0074] Further, in step 2.4, it is judged whether the laser output frequency corresponding to the main control current driving voltage U set and the set temperature T is in the center region of the servo control range of the corresponding acetylene molecular absorption peak, which includes:

[0075] Step 2.401, it is judged whether abs(LD ScanPoint -Curve min )<1 / 4*(Curve max -Curve min ) is true, 1 / 4 can be selected according to the actual situation, if yes, it is judged that the laser output frequency is in the servo control range of the acetylene molecular locking absorption peak, otherwise, it is judged that it deviates from the servo control range and needs to be corrected;

[0076] Step 2.402, before correction, the correction direction needs to be judged and the offset amount needs to be calculated, if LD ScanPoint -LD ScanMin >0, U set needs to be increased, corresponding to increasing the laser output wavelength; LD ScanPoint -LD ScanMin <0, corresponding to decreasing U set ; the correction amount ΔU set =k*abs(LD ScanPoint -LD ScanMin ), the size of k is proportional to the current modulation coefficient of the characteristic parameters of the tunable semiconductor laser.

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

[0078] Further, such as Figure 3 In steps 2.3 and 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 in 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 triangle wave scans downward based on the current value until the demodulation value of the frequency identification 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 jump into the pre-processing process.

[0081] If not, the current control module 13 selects B3, corresponding to the current control voltage U set The triangle 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 jump into the pre-processing process.

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

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

[0084] In the present invention, frequency stabilization methods based on feedback from the absorption spectrum of acetylene molecules can be divided into two types, based on feedback from the saturated absorption spectrum of acetylene molecules and based on feedback from the linear absorption spectrum of acetylene molecules, depending on the absorption state of the acetylene molecules. The frequency stabilization method based on feedback from the saturated absorption spectrum of acetylene molecules relies on the saturated absorption state of acetylene molecules at high light intensities, while the frequency stabilization method based on feedback from the linear absorption spectrum of acetylene molecules relies on the linear absorption of acetylene molecules at low light intensities. Saturated absorption frequency stabilization generally provides higher frequency stability and is suitable for high-precision applications; linear absorption frequency stabilization is suitable for applications with lower frequency stability requirements and has lower optical system requirements compared to saturated absorption. Both technologies are widely used in fields such as optical communications, spectral analysis, and lidar.

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

[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 feedback of the linear absorption spectrum characteristics of acetylene molecules. The system structure of a frequency stabilization method based on the feedback of the saturated absorption spectrum characteristics 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 merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the 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 fall within the scope of protection determined by the claims of the present invention.

Claims

1. A frequency stabilization system based on the feedback of the linear absorption spectrum characteristics of acetylene molecules, characterized in that: The invention 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 microcomputer module comprises a temperature control module (10), a single chip microcomputer automatic locking module (11), a PI control module (12) and a current control module (13); The FPGA unit includes 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 sequentially connected; the photodetector (4) is sequentially connected 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 microcomputer automatic locking module (11), and the single-chip microcomputer 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 the digital quantity into the frequency identification module (8); The frequency identification module (8) is used to receive a 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); The temperature control module (10) includes A1 and A2 programs; The current control module (13) includes B1, B2, B3, and B4 programs; 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; 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 according to 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). 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 conversion by an analog-to-digital converter (6), the signal enters a frequency identification module (8) of an FPGA unit with a sinusoidal signal (7) of the same source as the laser modulation signal, and is phase-locked amplified to obtain a laser frequency identification error signal. The second step is to perform preprocessing 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 within the range of T±T0 through the TEC module (14) to obtain a complete frequency discrimination curve, T is the laser temperature lock value set actively, and T0 is the temperature change amount that can be selected according to actual conditions; 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 As the center, the output range of the frequency discrimination voltage output module (9) is U min to U max A linear scanning voltage is generated, and a current driving module (15) is controlled to drive the tunable semiconductor laser (1) to perform frequency scanning; 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. If it does not reach the upper threshold value, the program will jump to the lock-back procedure after the frequency stabilization is lost. If it reaches the upper threshold value, the output value of the frequency identification module (8) will start from the current voltage output value and move to the upper threshold value. min Linear scan in the direction; 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, the program jumps into the lock-back procedure after the frequency stabilization is lost. If it reaches it, the main control current drive voltage U stored in the single chip computer RAM is determined 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 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 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 center 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 error signal fluctuates around 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 to lock. 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. The frequency stabilization method based on the characteristic feedback of the linear absorption spectrum of acetylene molecules according to claim 2, characterized in that: In the second step, the frequency discrimination curve characteristics 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 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. The frequency stabilization method based on the characteristic feedback of the linear absorption spectrum of acetylene molecules according to claim 3, characterized in that: In step 2.4, determine the main control current drive voltage U stored in the MCU RAM set Whether the laser output frequency corresponding to the set temperature T is within the center 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 corresponding main control current driving voltage U is reduced 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, characterized in that: In steps 2.3 and 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, characterized in that: In steps 2.3 and 2.4, the relocking procedure after 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) output. 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 triangle wave is scanned 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 jump into the pre-processing process; If not, the current control module (13) selects B3, corresponding to the main control voltage U set The triangle 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 jump into the pre-processing process.

7. A frequency stabilization method based on characteristic feedback of the saturated absorption spectrum of acetylene molecules, based on the frequency stabilization method based on characteristic feedback of the linear absorption spectrum of acetylene molecules according to claim 2, 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 photodetector (4) and are converted into an absorption peak signal of the gas chamber gas that eliminates the Doppler frequency shift background. After conversion 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, and are phase-locked amplified to extract the third harmonic to obtain a laser frequency identification error signal. Then execute steps 2 to 4.

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