A frequency discriminator locking point drift elimination laser frequency stabilization method based on frequency curve peak detection

Abstract

The application discloses a frequency discrimination locking point drift elimination laser frequency stabilization method based on frequency discrimination curve peak value detection and belongs to the technical field of semiconductor laser frequency stabilization control and ultra-precision instrument manufacturing. In order to solve the problem that the center frequency is difficult to stabilize when a micro probe laser interferometer light source is tuned in a large range and high bandwidth, the application comprises the following steps: a frequency discrimination locking point drift elimination laser frequency stabilization system based on frequency discrimination curve peak value detection is built; a digital electric signal containing frequency deviation information is obtained through operation and is input into a signal processing and controller FPGA to obtain a frequency discrimination signal containing frequency error information; a coarse adjustment stage and a fine step optimization stage of frequency discrimination curve locking point drift elimination are executed; an error calculation module completes the frequency discrimination curve locking point drift elimination; a feedback control switch between a closed PI control module and a first digital-to-analog converter is closed; and the driving current and temperature of a tunable semiconductor DFB laser are adjusted by a laser driver, so that the laser frequency is stabilized at the locking point.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor laser frequency stabilization control and ultra-precision instrument manufacturing technology, specifically relating to a laser frequency stabilization method based on frequency discrimination curve peak detection to eliminate frequency locking point drift. Background Technology

[0002] With the development of various laser applications, the requirements for laser frequency stability are becoming increasingly stringent. In fields such as lidar, fiber optic communication, and spectroscopy, frequency stability directly affects the system's performance and accuracy. Wavelength modulation technology is increasingly used in laser frequency stabilization. By introducing appropriate modulation into the laser, some noise and interference in the low-frequency band can be effectively avoided. Taking the micro-probe fiber laser interferometer, a representative of the new generation of ultra-precision laser interferometry instruments, as an example, when using it for high-speed, high-precision displacement measurement, the wavelength of its laser source needs to be tuned over a wide range and with a high bandwidth. However, for the distributed feedback semiconductor (DFB) laser in the micro-probe fiber laser interferometer, modulation of the laser wavelength generates additional undesirable phenomena such as intensity-dependent modulation and carrier phase delay. Furthermore, this phenomenon becomes more severe as the laser wavelength modulation speed and bandwidth increase. If not addressed, it can reduce the sensitivity of the frequency stabilization control system or even prevent laser frequency stabilization control.

[0003] Frequency stabilization technology can be divided into passive and active frequency stabilization, depending on whether a stable frequency reference standard is available. Passive frequency stabilization technology mainly aims to reduce frequency fluctuations caused by factors such as operating current, temperature, and environmental vibration. Fluctuations in drive current and laser tube operating temperature are two major factors affecting the stability of the output wavelength. Passive frequency stabilization technology can achieve limited laser frequency stability. Therefore, active frequency stabilization technology is needed to control the laser's output wavelength at a standard reference. The most commonly used external reference standard is a standard FP cavity or a gas atomic absorption spectrum. When using an internally modulated semiconductor laser, the emitted light passes through an atomic gas cell. Through lock-in amplification, an error signal, also known as a frequency discrimination curve, can be obtained between the locked position of the laser and the gas molecule absorption spectrum. This error signal is then fed back to the laser tube's drive current and drive temperature control via PID control, achieving stable control of the laser output center frequency. The shape and position of the frequency discrimination curve are affected by the laser's modulation speed and modulation bandwidth.

[0004] The invention patent with application number 202311467885.1 and invention title "Method and System for Frequency Stabilization of Tuned Light Source Based on Characteristic Curve Reconstruction" considers that the distortion of the frequency discrimination curve will cause the frequency stabilization lock point to deviate from the reference point. It calculates a new frequency stabilization lock point to replace the traditional scheme that uses zero as the frequency stabilization lock point. However, the calculated new lock point is affected by the magnitude of the absorptivity of the acetylene target absorption peak. This value is affected by factors such as ambient temperature and air pressure, and different target absorption peaks correspond to different absorptivity. Therefore, it has the problem of limited applicability and does not essentially eliminate the influence of the distortion of the frequency discrimination curve, which will lead to low sensitivity of frequency stabilization control. Summary of the Invention

[0005] This invention addresses the problem of difficulty in stabilizing the center frequency of a microprobe laser interferometer light source under wide-range, high-bandwidth tuning. It proposes a laser frequency stabilization method based on peak detection of the frequency discrimination curve to eliminate drift at the frequency discrimination locking point.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A laser frequency stabilization method for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve includes the following steps:

[0008] S1. Construct a laser frequency stabilization system for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve, including a tunable semiconductor DFB laser, an optical isolator, an optical fiber coupler, an acetylene gas chamber, a photodetector, an analog-to-digital converter (ADC), a signal processing and control FPGA, a direct digital frequency synthesizer (DDS), a second digital-to-analog converter (DAC), a first DAC, and a laser driver;

[0009] S2. Run a laser frequency stabilization system for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve to obtain a digital electrical signal containing frequency deviation information;

[0010] S3. Input the digital electrical signal containing frequency deviation information obtained in step S2 into the signal processing and controller FPGA to obtain a frequency discrimination signal containing frequency error information;

[0011] S4. For the frequency discrimination signal containing frequency error information obtained in step S3, a coarse adjustment stage for eliminating drift at the frequency discrimination curve locking point is performed. The signal processing and controller FPGA generates a cosine signal. The variable phase φ in the cosine signal is discretely scanned in steps of 18° within the range of 0° to 360°, and the peak-to-peak value of the frequency discrimination curve corresponding to each phase point is recorded. The extreme values ​​and the maximum absolute values ​​of the frequency discrimination curve corresponding to each phase point. Then, the phase difference between optical frequency modulation and optical intensity modulation is obtained through difference calculation. ;

[0012] S5. After the coarse adjustment stage, a fine-step optimization stage is performed, adjusting the variable phase φ in the cosine signal. and Centered on the carrier, each step is made in increments of +9° and -9° to identify and record whether a new peak-to-peak value, extreme value, and absolute value of the frequency discrimination curve appear, and update the carrier phase delay and the phase difference between optical frequency modulation and optical intensity modulation.

[0013] S6. Based on the updated carrier phase delay and the phase difference between optical frequency modulation and optical intensity modulation obtained in step S5, the error calculation module completes the frequency discrimination curve lock point drift elimination;

[0014] S7. After eliminating the drift of the frequency discrimination curve lock point based on step S6, close the feedback control switch between the PI control module and the first digital-to-analog converter, and adjust the driving current and temperature of the laser driver for the tunable semiconductor DFB laser so that the laser frequency is stabilized at the lock point.

[0015] Furthermore, in step S1, the tunable semiconductor DFB laser is sequentially connected to an optical isolator, an optical fiber coupler, an acetylene gas chamber, a photodetector, an analog-to-digital converter (ADC), a signal processing and control FPGA, a first digital-to-analog converter (DAC), and a laser driver. The laser driver is connected to the tunable semiconductor DFB laser, the tunable semiconductor DFB laser is connected to a second DAC, the second DAC is connected to a direct digital frequency synthesizer (DDS), and the DDS is connected to the signal processing and control FPGA.

[0016] Furthermore, the signal processing and controller FPGA mentioned in step S1 includes a multiplier, a cosine signal generation module (COS), a distortion correction module, a low-pass filter module (LPF), an error calculation module, and a PI control module. The multiplier in the signal processing and controller FPGA is connected to the cosine signal generation module (COS) and the low-pass filter module (LPF), the low-pass filter module (LPF) is connected to the distortion correction module and the error calculation module, the distortion correction module is connected to the cosine signal generation module (COS) and the error calculation module, and the error calculation module is connected to the PI control module.

[0017] Furthermore, the splitting ratio of the fiber coupler is 90:10, with 90% of the intensity of the main beam in the incident light used as the output light for subsequent measurement optical path, and the remaining 10% intensity of the branch light injected into the acetylene gas chamber as the detection signal light.

[0018] Furthermore, in step S2, a laser frequency stabilization system for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve is implemented. The continuous laser output from the tunable semiconductor DFB laser, modulated by the second digital-to-analog converter, is injected into the acetylene gas chamber after the back-reflection light interference is suppressed by the optical isolator and then incident on the fiber coupler. The outgoing light from the acetylene gas chamber is converted by a photodetector to generate an analog electrical signal containing frequency deviation information. This analog electrical signal is then digitally sampled by the analog-to-digital converter (ADC) to obtain a digital electrical signal containing frequency deviation information.

[0019] Furthermore, step S3 involves inputting the digital electrical signal containing frequency deviation information obtained in step S2 into the signal processing and controller FPGA. This digital electrical signal containing frequency deviation information is then compared with a cosine signal generated by the cosine signal generation module COS. The mixing operation is completed in the multiplier. After the high-frequency components are filtered out by the low-pass filter module LPF, a frequency discrimination signal containing frequency error information is obtained. After passing through the error calculation module and the PI control module, the frequency discrimination error digital control signal is calculated. This signal is converted into an analog control signal by the first digital-to-analog converter DAC and applied to the laser driver. The laser driver controls the temperature and current of the tunable semiconductor DFB laser, changing the laser output frequency of the tunable semiconductor DFB laser and initially locking the laser center frequency in the linear working region of the acetylene absorption peak.

[0020] Furthermore, in step S4, the laser driver performs active temperature scanning on the tunable semiconductor DFB laser, controlling the laser output frequency variation range of the tunable semiconductor DFB laser to cover the complete acetylene absorption peak, and obtains a complete frequency discrimination curve after passing through the low-pass filter module LPF.

[0021] The distortion correction module controls the cosine signal generation module (COS) to generate the cosine signal. The variable phase φ is discretely scanned in steps of 18° within the range of 0° to 360°, and the peak value of the frequency discrimination curve is compared at each phase point. Valley of the frequency discrimination curve Perform statistical analysis to identify and record the peak-to-peak value of the frequency discrimination curve. Maximum value, extreme values ​​and absolute values ​​of the frequency discrimination curve The maximum value, the phase corresponding to the peak-to-peak value of the frequency discrimination curve. Recorded as The extreme values ​​and the maximum absolute values ​​of the frequency discrimination curve correspond to the phase. Recorded as Through difference operation Seek Size, of which This is the carrier phase delay.

[0022] Furthermore, in step S6, let Variable phase in The frequency discrimination curve's locking point is precisely aligned with the reference point. The error calculation module receives the frequency discrimination signal containing frequency error information and divides it by... To achieve elimination The slope of the linear region in the center of the frequency discrimination curve is increased to improve the system control sensitivity, which is beneficial to improve the stability of the laser frequency and eliminate the drift of the frequency discrimination lock point.

[0023] Furthermore, in step S6, the locking point of the frequency discrimination curve is such that... The corresponding frequency point, with the reference point being the frequency point corresponding to the acetylene absorption peak, is represented by the frequency discrimination signal after eliminating the frequency discrimination lock point drift as follows:

[0024]

[0025] in, To achieve the center frequency of the laser output of a tunable semiconductor DFB laser, For the modulation frequency range, To pinpoint the frequency corresponding to the acetylene absorption peak. The acetylene transmission spectrum is at half maximum and half width at half maximum. I represents the normalized absorption rate at the center of the transmission spectral line, and I is a digital electrical signal containing frequency deviation information.

[0026] The beneficial effects of this invention are:

[0027] This invention discloses a laser frequency stabilization method based on peak detection of the frequency discrimination curve to eliminate drift at the frequency discrimination lock point. This method addresses the challenge of simultaneously achieving large-amplitude, high-bandwidth modulation and high-precision frequency stabilization using tuned light sources in micro-probe fiber laser interferometers used for large-range, high-bandwidth dynamic displacement measurements. By fixing the laser frequency lock point at the zero point of the frequency discrimination curve, it eliminates the influence of accompanying intensity modulation and carrier phase delay on laser frequency stability under large-range, high-bandwidth modulation. It is universally applicable to 54 acetylene absorption lines within a wide bandwidth of 1512nm-1542nm, achieving precise positioning of the gas molecule absorption lock point. Furthermore, because the influence of intensity-accompanying modulation and carrier phase delay on the distortion of the frequency discrimination curve is completely eliminated at the source, the slope of the linear region in the center of the frequency discrimination curve is restored, improving the system's control sensitivity and thus enhancing laser frequency stability. Attached Figure Description

[0028] Figure 1 This is a flowchart of a laser frequency stabilization method for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve, as described in this invention.

[0029] Figure 2This is a schematic diagram of the laser frequency stabilization system for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve, as described in this invention.

[0030] Figure 3 This is a schematic diagram of the internal FPGA module of the signal processing and controller of the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described specific embodiments are merely a part of the embodiments of the invention, and not all of them. The components of the specific embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations, and the invention may also have other embodiments.

[0032] Therefore, the following detailed description of specific embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected specific embodiments of the invention. All other specific embodiments obtained by those skilled in the art based on these specific embodiments without inventive effort are within the scope of protection of this invention.

[0033] To further understand the invention's content, features, and effects, the following specific embodiments are provided, along with accompanying drawings. Figure 1 -Appendix Figure 3 Detailed explanation is as follows:

[0034] Example 1:

[0035] A laser frequency stabilization method for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve includes the following steps:

[0036] S1. Construct a laser frequency stabilization system for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve, including a tunable semiconductor DFB laser 1, an optical isolator 2, an optical fiber coupler 3, an acetylene gas chamber 4, a photodetector 5, an analog-to-digital converter (ADC) 6, a signal processing and control FPGA 7, a direct digital frequency synthesizer (DDS) 8, a second digital-to-analog converter (DAC) 9, a first DAC 10, and a laser driver 11;

[0037] Furthermore, in step S1, the tunable semiconductor DFB laser 1 is sequentially connected to an optical isolator 2, an optical fiber coupler 3, an acetylene gas chamber 4, a photodetector 5, an analog-to-digital converter (ADC) 6, a signal processing and control FPGA 7, a first digital-to-analog converter 10, and a laser driver 11. The laser driver 11 is connected to the tunable semiconductor DFB laser 1, the tunable semiconductor DFB laser 1 is connected to a second digital-to-analog converter 9, the second digital-to-analog converter 9 is connected to a direct digital frequency synthesizer (DDS) 8, and the direct digital frequency synthesizer (DDS) 8 is connected to the signal processing and control FPGA 7.

[0038] The signal processing and controller FPGA7 mentioned in step S1 includes a multiplier 12, a cosine signal generation module COS13, a distortion correction module 14, a low-pass filter module LPF15, an error calculation module 16, and a PI control module 17. The multiplier 12 in the signal processing and controller FPGA7 is connected to the cosine signal generation module COS13 and the low-pass filter module LPF15, the low-pass filter module LPF15 is connected to the distortion correction module 14 and the error calculation module 16, the distortion correction module 14 is connected to the cosine signal generation module COS13 and the error calculation module 16, and the error calculation module 16 is connected to the PI control module 17.

[0039] The optical fiber coupler 3 has a splitting ratio of 90:10. 90% of the intensity of the main beam in the incident light is used as the output light for subsequent measurement optical path, and the remaining 10% intensity of the branch light is injected into the acetylene gas chamber as the detection signal light.

[0040] Furthermore,

[0041] The signal processing and controller FPGA7 controls the direct digital frequency synthesizer DDS8, which is connected to the tunable semiconductor DFB laser 1 via digital-to-analog converter DAC29 to modulate the laser output frequency. The signal processing and controller FPGA7 receives the digital signal containing frequency error information converted by analog-to-digital converter ADC6, calculates the frequency discrimination error digital control signal, and converts it into an analog control signal through digital-to-analog converter DAC110 to control the laser driver 11 to complete the frequency stabilization control of the tunable semiconductor DFB laser 1. The frequency stabilization control of the tunable semiconductor DFB laser 1 by the laser driver 11 is achieved simultaneously through temperature control and current control.

[0042] The COS13 cosine signal generation module outputs two cosine signals, one of which... One circuit controls the direct digital frequency synthesizer DDS8, while the other circuit controls the distortion correction module 14, with the output including variable phase. cosine signal The digital signal containing frequency error information obtained by the analog-to-digital converter ADC6 Multiplication is performed in multiplier 12; multiplier 12 is connected to low-pass filter module LPF15; the output of low-pass filter module LPF15 is divided into two paths, one path is connected to distortion correction module 14, and the other path is connected to error calculation module 16 and PI control module 17 in sequence. PI control module 17 calculates the frequency discrimination error digital control signal.

[0043] S2. Run a laser frequency stabilization system for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve to obtain a digital electrical signal containing frequency deviation information;

[0044] Furthermore, in step S2, a laser frequency stabilization system for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve is implemented. The continuous laser output from the tunable semiconductor DFB laser 1, modulated by the second digital-to-analog converter 9, is injected into the acetylene gas chamber 4 after the back-reflection light interference is suppressed by the optical isolator 2 and then incident on the fiber optic coupler 3. The outgoing light from the acetylene gas chamber 4 is photoelectrically converted by the photodetector 5 to generate an analog electrical signal containing frequency deviation information. This signal is then digitally sampled by the analog-to-digital converter ADC 6 to obtain a digital electrical signal containing frequency deviation information.

[0045] Furthermore, the output frequency of the tunable semiconductor DFB laser 1 modulated by the digital-to-analog converter DAC29 is... ;

[0046] The digital electrical signal containing frequency deviation information after digital sampling by the analog-to-digital converter ADC6 is... , Performing a Taylor expansion at frequency v and combining like terms yields:

[0047]

[0048] in, To achieve the center frequency of the laser output of a tunable semiconductor DFB laser, Where m is the modulation frequency range and m is the modulation coefficient associated with the light intensity. The phase difference between optical frequency modulation and optical intensity modulation. Carrier phase delay (CPD), This is the angular frequency corresponding to the modulation signal output by the digital-to-analog converter DAC2. , , and These are the first, second, third, and fourth derivatives of I(v), respectively, and so on.

[0049] S3. Input the digital electrical signal containing frequency deviation information obtained in step S2 into the signal processing and controller FPGA7 to obtain a frequency discrimination signal containing frequency error information;

[0050] Furthermore, step S3 involves inputting the digital electrical signal containing frequency deviation information obtained in step S2 into the signal processing and controller FPGA7. This digital electrical signal containing frequency deviation information is then compared with a cosine signal generated by the cosine signal generation module COS13. The mixing operation is completed in multiplier 12. After the high-frequency components are filtered out by low-pass filter module LPF15, a frequency discrimination signal containing frequency error information is obtained. After passing through error calculation module 16 and PI control module 17, the frequency discrimination error digital control signal is calculated. It is converted into an analog control signal by first digital-to-analog converter DAC10 and applied to laser driver 11. Laser driver 11 controls the temperature and current of tunable semiconductor DFB laser 1, changes the laser output frequency of tunable semiconductor DFB laser 1, and initially locks the laser center frequency in the linear working region of acetylene absorption peak.

[0051] Furthermore, after the high-frequency components are filtered out by the low-pass filter module LPF and higher-order derivative terms are ignored, retaining only the first-order derivative term, the frequency discrimination signal containing frequency error information is obtained as follows:

[0052]

[0053] in, This is a function representing the acetylene transmission curve. To determine the center frequency of the tunable semiconductor DFB laser output, the derivative of the acetylene transmission curve function with respect to frequency is taken, and the derivative is substituted into the above equation to obtain the final frequency discrimination signal:

[0054]

[0055] in, The normalized absorption rate at the center of the transmission spectral line. The acetylene transmission spectrum is at half maximum and half width at half maximum. In order to pinpoint the frequency corresponding to the acetylene absorption peak;

[0056] Let the first term be The second item is Obviously , They are respectively based on odd and even functions centered on the center, for Taking the derivative, we can find the local maxima and local minima of the first term as follows:

[0057]

[0058]

[0059]

[0060] ;

[0061] S4. For the frequency discrimination signal containing frequency error information obtained in step S3, a coarse adjustment stage for eliminating drift at the frequency discrimination curve lock point is performed. The signal processing and controller FPGA7 generates a cosine signal. The variable phase φ in the cosine signal is discretely scanned in steps of 18° within the range of 0° to 360°, and the peak-to-peak value of the frequency discrimination curve corresponding to each phase point is recorded. The extreme values ​​and the maximum absolute values ​​of the frequency discrimination curve corresponding to each phase point. Then, the phase difference between optical frequency modulation and optical intensity modulation is obtained through difference calculation. ;

[0062] Furthermore, in step S4, the laser driver 11 performs active temperature scanning on the tunable semiconductor DFB laser 1, controlling the laser output frequency variation range of the tunable semiconductor DFB laser 1 to cover the complete acetylene absorption peak, and obtains a complete frequency discrimination curve after passing through the low-pass filter module LPF15.

[0063] The distortion correction module 14 controls the cosine signal generation module COS13 to generate the cosine signal. The variable phase φ is discretely scanned in steps of 18° within the range of 0° to 360°, and the peak value of the frequency discrimination curve is compared at each phase point. Valley of the frequency discrimination curve Perform statistical analysis to identify and record the peak-to-peak value of the frequency discrimination curve. Maximum value, extreme values ​​and absolute values ​​of the frequency discrimination curve The maximum value, the phase corresponding to the peak-to-peak value of the frequency discrimination curve. Recorded as The extreme values ​​and the maximum absolute values ​​of the frequency discrimination curve correspond to the phase. Recorded as Through difference operation Seek Size, of which This is the carrier phase delay.

[0064] Furthermore, each phase point corresponds to the peak-to-peak value of the frequency discrimination curve. That is:

[0065] ;

[0066] Extreme values ​​and absolute values That is:

[0067] ;

[0068] S5. After the coarse adjustment stage, a fine-step optimization stage is performed, adjusting the variable phase φ in the cosine signal. and Centered on the carrier, each step is made in increments of +9° and -9° to identify and record whether a new peak-to-peak value, extreme value, and absolute value of the frequency discrimination curve appear, and update the carrier phase delay and the phase difference between optical frequency modulation and optical intensity modulation.

[0069] S6. Based on the updated carrier phase delay and the phase difference between optical frequency modulation and optical intensity modulation obtained in step S5, the error calculation module 16 completes the frequency discrimination curve lock point drift elimination;

[0070] Furthermore, in step S6, let Variable phase in The frequency discrimination curve's locking point is precisely aligned with the reference point. Simultaneously, the error calculation module 16 receives the frequency discrimination signal containing frequency error information and divides it by... To achieve elimination The slope of the linear region in the center of the frequency discrimination curve is increased to improve the system control sensitivity, which is beneficial to improve the stability of the laser frequency and eliminate the drift of the frequency discrimination lock point.

[0071] Furthermore, in step S6, the locking point of the frequency discrimination curve is such that... The corresponding frequency point, with the reference point being the frequency point corresponding to the acetylene absorption peak, is represented by the frequency discrimination signal after eliminating the frequency discrimination lock point drift as follows:

[0072] ;

[0073] in, To achieve the center frequency of the laser output of a tunable semiconductor DFB laser, For the modulation frequency range, To pinpoint the frequency corresponding to the acetylene absorption peak. The acetylene transmission spectrum is at half maximum and half width at half maximum. I represents the normalized absorption rate at the center of the transmission spectral line, and I is a digital electrical signal containing frequency deviation information.

[0074] S7. After eliminating the drift of the frequency discrimination curve lock point based on step S6, close the feedback control switch between the PI control module 17 and the first digital-to-analog converter 10, and adjust the driving current and temperature of the laser driver 11 to the tunable semiconductor DFB laser 1 so that the laser frequency is stabilized at the lock point.

[0075] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0076] Although this application has been described above with reference to specific embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of this application. In particular, as long as there is no structural conflict, the features in the specific embodiments disclosed in this application can be combined with each other in any way. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, this application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A laser frequency stabilization method for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve, characterized in that, Includes the following steps: S1. Construct a laser frequency stabilization system for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve, including a tunable semiconductor DFB laser (1), an optical isolator (2), an optical fiber coupler (3), an acetylene gas chamber (4), a photodetector (5), an analog-to-digital converter (ADC) (6), a signal processing and control FPGA (7), a direct digital frequency synthesizer (DDS) (8), a second digital-to-analog converter (9), a first digital-to-analog converter (10), and a laser driver (11). The signal processing and controller FPGA (7) mentioned in step S1 includes a multiplier (12), a cosine signal generation module COS (13), a distortion correction module (14), a low-pass filter module LPF (15), an error calculation module (16), and a PI control module (17); the multiplier (12) in the signal processing and controller FPGA (7) is connected to the cosine signal generation module COS (13) and the low-pass filter module LPF (15) respectively, the low-pass filter module LPF (15) is connected to the distortion correction module (14) and the error calculation module (16) respectively, the distortion correction module (14) is connected to the cosine signal generation module COS (13) and the error calculation module (16) respectively, and the error calculation module (16) is connected to the PI control module (17); S2. Run the frequency discrimination locking point drift elimination laser frequency stabilization system based on frequency discrimination curve peak detection to obtain a digital electrical signal containing frequency deviation information; S3. Input the digital electrical signal containing frequency deviation information obtained in step S2 into the signal processing and controller FPGA (7) to obtain a frequency discrimination signal containing frequency error information; S4. For the frequency discrimination signal containing frequency error information obtained in step S3, a coarse adjustment stage for eliminating drift at the frequency discrimination curve locking point is performed. The signal processing and controller FPGA (7) generates a cosine signal, and the variable phase in the cosine signal... Offline scanning was performed within the range of 0° to 360° with a step size of 18°, and the peak-to-peak value of the frequency discrimination curve corresponding to each phase point was recorded. The maximum absolute value of the sum of the extreme values ​​of the frequency discrimination curve corresponding to each phase point. Then, the phase difference between optical frequency modulation and optical intensity modulation is obtained through difference calculation. ; S5. After the coarse adjustment stage, a fine-step optimization stage is performed to adjust the variable phase in the cosine signal. by and Centered on the carrier, each step is made in increments of +9° and -9° to identify and record whether a new peak-to-peak value, extreme value, and absolute value of the frequency discrimination curve appear, and update the carrier phase delay and the phase difference between optical frequency modulation and optical intensity modulation. S6. Based on the updated carrier phase delay and the phase difference between optical frequency modulation and optical intensity modulation obtained in step S5, the error calculation module (16) completes the frequency discrimination curve lock point drift elimination; S7. After eliminating the drift of the frequency discrimination curve lock point based on step S6, close the feedback control switch between the PI control module (17) and the first digital-to-analog converter (10), and adjust the driving current and temperature of the laser driver (11) on the tunable semiconductor DFB laser (1) so that the laser frequency is stabilized at the lock point.

2. The laser frequency stabilization method for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve according to claim 1, characterized in that, In step S1, the tunable semiconductor DFB laser (1) is sequentially connected to an optical isolator (2), an optical fiber coupler (3), an acetylene gas chamber (4), a photodetector (5), an analog-to-digital converter (ADC) (6), a signal processing and control FPGA (7), a first digital-to-analog converter (10), and a laser driver (11). The laser driver (11) is connected to the tunable semiconductor DFB laser (1). The tunable semiconductor DFB laser (1) is connected to a second digital-to-analog converter (9). The second digital-to-analog converter (9) is connected to a direct digital frequency synthesizer (DDS) (8). The direct digital frequency synthesizer (DDS) (8) is connected to the signal processing and control FPGA (7).

3. The laser frequency stabilization method for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve according to claim 2, characterized in that, The optical fiber coupler (3) has a splitting ratio of 90:

10. The main beam with 90% intensity of the incident light is used as the output light for subsequent measurement optical path, and the branch light with the remaining 10% intensity is injected into the acetylene gas chamber as the detection signal light.

4. The laser frequency stabilization method for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve according to claim 3, characterized in that, Step S2 runs the frequency discrimination locking point drift elimination laser frequency stabilization system based on frequency discrimination curve peak detection. The continuous laser output from the tunable semiconductor DFB laser (1) modulated by the second digital-to-analog converter (9) is injected into the acetylene gas chamber (4) after the back reflection light interference is suppressed by the optical isolator (2). The light emitted from the acetylene gas chamber (4) is photoelectric converted by the photodetector (5) to generate an analog electrical signal containing frequency deviation information. Then, it is digitally sampled by the analog-to-digital converter (ADC) (6) to obtain a digital electrical signal containing frequency deviation information.

5. The laser frequency stabilization method for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve according to claim 4, characterized in that, Step S3 involves inputting the digital electrical signal containing frequency deviation information obtained in step S2 into the signal processing and controller FPGA (7). The digital electrical signal containing frequency deviation information is then compared with a cosine signal generated by the cosine signal generation module COS (13). The mixing operation is completed in the multiplier (12). After the high frequency components are filtered out by the low-pass filter module LPF (15), the frequency discrimination signal containing frequency error information is obtained. The frequency discrimination error digital control signal is calculated by the error calculation module (16) and the PI control module (17). It is converted into an analog control signal by the first digital-to-analog converter (10) and applied to the laser driver (11). The laser driver (11) controls the temperature and current of the tunable semiconductor DFB laser (1) and changes the laser output frequency of the tunable semiconductor DFB laser (1) to initially lock the laser center frequency in the linear working region of the acetylene absorption peak.

6. The laser frequency stabilization method for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve according to claim 5, characterized in that, In step S4, the laser driver (11) performs active temperature scanning on the tunable semiconductor DFB laser (1) and controls the laser output frequency of the tunable semiconductor DFB laser (1) to cover the complete acetylene absorption peak. After passing through the low-pass filter module LPF (15), a complete frequency discrimination curve is obtained. The distortion correction module (14) controls the cosine signal generation module COS (13) to generate the cosine signal. The variable phase Offline scanning was performed within the range of 0° to 360° with a step size of 18°, and the peak value of the frequency discrimination curve was compared at each phase point. Valley of the frequency discrimination curve Perform statistical analysis to identify and record the peak-to-peak value of the frequency discrimination curve. The absolute value of the sum of the maximum value and the extreme values ​​of the frequency discrimination curve The maximum value, the phase corresponding to the peak-to-peak value of the frequency discrimination curve. Recorded as The maximum absolute value of the sum of the extreme values ​​of the frequency discrimination curve corresponds to the phase. Recorded as Through difference operation Seek Size, of which This is the carrier phase delay.

7. The laser frequency stabilization method for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve according to claim 6, characterized in that, In step S6, let Variable phase in The locking point of the frequency discrimination curve is made to coincide precisely with the reference point. The error calculation module (16) receives the frequency discrimination signal containing frequency error information and divides it by 1 / 2. To achieve elimination The slope of the linear region in the center of the frequency discrimination curve is increased to improve the system control sensitivity, which is beneficial to improve the stability of the laser frequency and eliminate the drift of the frequency discrimination lock point.

8. The laser frequency stabilization method for eliminating drift at the frequency discrimination locking point based on peak detection of the frequency discrimination curve according to claim 7, characterized in that, The locking point of the frequency discrimination curve in step S6 is such that... The corresponding frequency point, with the reference point being the frequency point corresponding to the acetylene absorption peak, is represented by the frequency discrimination signal after eliminating the frequency discrimination lock point drift as follows: in, To achieve the center frequency of the laser output of a tunable semiconductor DFB laser, For the modulation frequency range, To pinpoint the frequency corresponding to the acetylene absorption peak. The acetylene transmission spectrum is at half maximum and half width at half maximum. I represents the normalized absorbance of the acetylene transmission line center, and I is a digital electrical signal containing frequency deviation information.

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