Laser automatic frequency locking system based on similarity identification spectrum

Abstract

The utility model relates to a laser automatic frequency locking system based on similarity identification spectrum, comprising a laser, a spectrum module, a digital PID feedback controller and an automatic frequency locking operation system, the automatic frequency locking operation system is used for determining a locking point of a received spectrum signal based on a similarity identification algorithm, and determining a corresponding automatic frequency locking parameter based on the locking point, and performing PID locking control on the laser by the digital PID feedback controller based on the automatic frequency locking parameter of the locking point. The scheme has the advantages of small environmental influence interference, more stable working state, wide application range and high working efficiency.

Description

Technical Field

[0001] The utility model relates to the technical field of laser frequency locking, in particular to a laser automatic frequency locking system based on similarity recognition spectrum. Background Art

[0002] Lasers play many important roles in both scientific research and product development. For example, quantum gyroscope systems use Doppler cooling or Raman cooling technology to cool and trap atoms. By applying precisely timed laser pulses to the atomic beam, the quantum state of the atoms can be manipulated to cause interference, and the interference pattern can be used to calculate the high-precision rotational acceleration value. Although the laser light produced by ordinary commercial lasers is monochromatic, its line width is generally tens to hundreds of megahertz, and its wavelength has a longer-term drift in a larger range, which does not meet the needs of scientific research and engineering applications in the field of quantum precision measurement. At this time, it is necessary to lock the frequency of the laser near a specific frequency point, that is, laser frequency locking technology (hereinafter referred to as laser frequency locking). Whether the frequency of the laser is stable or not determines the accuracy of atomic interferometry measurement.

[0003] The main function of laser frequency locking is to control the frequency of the laser so that it is locked to the characteristic frequency reference of the spectrum, such as an optical reference cavity or atomic transition frequency, in order to maintain a stable output of the laser frequency.

[0004] In practical applications, laser frequency locking usually adopts various locking techniques, such as PHD locking, heterodyne offset locking, jitter locking, saturated absorption spectroscopy locking (SAS), modulation transfer spectroscopy locking (MTS), and frequency modulation spectroscopy locking (FMS). These techniques make the laser present a fixed frequency through feedback control mechanism.

[0005] At present, the method of laser frequency locking is usually to manually observe the spectral signal in the optical feedback loop and determine the locking point to set the corresponding locking voltage for the PID controller and then lock the laser frequency. However, since the frequency of the laser is very sensitive to the external environment, factors such as mechanical vibration and thermal fluctuations may affect the stability of the laser and cause the laser to be out of the locked state, resulting in the laser frequency locking being often unstable, so the opportunity to effectively detect and characterize the signal is very limited.

[0006] Therefore, if the laser can be automatically locked and can automatically find the required locking point after unlocking, it will greatly improve the stability and work efficiency of the laser system and improve the degree of automation. In many application fields with high requirements for laser frequency stability, such as: long-term continuous unattended observation of high-precision quantum gravimeters at seismic network stations; continuous mapping of dynamic absolute gravity on marine ships, etc. Stable laser frequency can greatly improve work efficiency and reliability of experimental data.

[0007] The Chinese invention application with publication number CN 116345287 A discloses a method, system and device for automatic frequency locking of laser signals. The method first performs a frequency sweep operation on the laser until an error signal is collected, and then outputs a triangular wave voltage signal to drive the laser. After obtaining the error signal curve, the PID control is started at the peak of the curve to keep the laser frequency at zero, so as to control the laser output frequency to be consistent with the transition frequency of the rubidium atom. The method of finding the locking point in the invention is too simple and single, and is easily interfered when looking for signal peaks. For example, when there are peaks of other spectral lines or peaks of noise signals, misjudgment may occur, resulting in the locked laser frequency not matching the required frequency, and it is still necessary to manually confirm whether it is locked on the required spectral line. In addition, the invention does not have the function of automatically relocking the laser after it is unlocked. It is easy to get out of the locked state in an environment with interference and vibration, and the reliability is not high.

[0008] The Chinese invention patent with the announcement number CN 109301687 B discloses a laser automatic frequency stabilization system based on the intelligent recognition technology of saturated absorption spectrum. The system includes a laser closed-loop locking circuit and an automatic relocking circuit. The closed-loop locking circuit is composed of an atomic absorption gas chamber, a frequency discriminator based on the saturated absorption spectrum, and a feedback controller to achieve closed-loop locking of the laser frequency; the automatic relocking circuit combines the pattern recognition technology in artificial intelligence with the classical optoelectronic technology, so that it can accurately and automatically tune the working state of the laser and search for the locking point in the saturated absorption spectrum. When the laser frequency is in a locked state, the laser closed-loop locking circuit keeps working to achieve the locking of the laser frequency; when the laser frequency is in an unlocked state, the relocking circuit relocks the laser frequency through a series of automated operations. It can achieve one-click automatic locking of the laser frequency and automatic relocking after loss of lock.

[0009] The system can achieve automatic laser frequency locking while taking into account the intelligent judgment of the locking point. It is a method that can achieve one-click automatic locking of the laser frequency and automatic relocking after loss of lock. The pattern recognition technology used in this method is essentially a saturation absorption spectrum recognition technology based on a support vector machine. The characteristic vectors in the saturation absorption spectrum are finally divided into positive and negative through a two-level classifier, thereby identifying the vector that needs to be locked. However, after the method identifies the corresponding saturation absorption peak, it needs to perform another convolution operation. By convolving different absorption peaks with the entire spectrum, the peak position of the result is used to determine the position of the locking point. Therefore, this method fails to achieve a completely intelligent search for the locking point of the laser frequency. At the same time, the support vector machine has certain limitations. When it is necessary to perform laser frequency locking on other spectra such as modulation transfer spectrum (MTS, modulation transfer spectrum can produce a monotonous error signal without Doppler background, avoiding the additional noise caused by directly modulating the laser; it has the advantages of high sensitivity, high resolution, and high error signal slope), frequency modulation spectrum (FMS, frequency modulation spectrum has strong anti-interference ability and stable transmission quality, can effectively resist external noise interference and achieve long-distance transmission), this method cannot be directly adapted. Utility Model Content

[0010] In order to solve the above problems, the purpose of the utility model is to provide a laser automatic frequency locking system based on similarity recognition spectrum.

[0011] A laser automatic frequency locking system based on similarity recognition spectrum, comprising:

[0012] A laser, including a laser light source and a laser controller, wherein the laser controller controls the laser light source to output an optical frequency signal to a spectrum module;

[0013] A spectrum module, comprising a fiber collimator, a first beam splitter, a second beam splitter, and an electro-optic modulator and a rubidium gas chamber arranged in parallel from the signal input direction to the signal output direction, wherein the emission end of the second beam splitter is connected to the modulation and demodulation module via a photodiode, the first output end of the modulation and demodulation module is connected to the photoelectric modulator, the first output end outputs a radio frequency modulated signal to the photoelectric modulator, the second output end of the modulation and demodulation module is connected to the digital PID feedback controller, and the second output end outputs a spectrum signal to the digital PID feedback controller;

[0014] A digital PID feedback controller is used to output a frequency sweep signal to the laser, and send a spectrum signal corresponding to the frequency sweep signal to the automatic frequency locking operation system, and at the same time perform PID control and lock the laser based on the automatic frequency locking parameters determined by the automatic frequency locking operation system;

[0015] The automatic frequency locking operation system is used to determine the locking point of the received spectral signal based on a similarity recognition algorithm, and determine the corresponding automatic frequency locking parameters based on the locking point.

[0016] Preferably, one input end of the modulation and demodulation module is the input end of the external reference signal, and the input reference signal is divided into two paths. The first signal is output to the electro-optical modulator as a signal of the required frequency of the electro-optical modulator; the second signal is used as a reference signal when the modulation and demodulation module demodulates.

[0017] Preferably, the modulation and demodulation module includes an operational amplifier and a demodulation chip; the operational amplifier is used to perform active bandpass filtering and voltage amplification on the electrical signal input via the photodiode; the demodulation chip is used to demodulate the electrical signal amplified by the operational amplifier based on the second signal as a reference signal.

[0018] Preferably, the digital PID feedback controller includes a microcontroller, a digital-to-analog converter and an analog-to-digital converter. The microcontroller is connected to the digital-to-analog converter and the analog-to-digital converter respectively. The output end of the digital-to-analog converter is connected to the laser. The microcontroller drives the digital-to-analog converter to lock the frequency of the laser. The input end of the analog-to-digital converter is connected to the output end of the spectrum. The microcontroller drives the analog-to-digital converter to read the spectrum signal in parallel at high speed and convert the read spectrum signal into a digital signal.

[0019] Preferably, the automatic frequency locking operation system comprises:

[0020] The spectrum scanning module is used to control the digital PID feedback controller to output a preset frequency sweep voltage to the laser;

[0021] A similarity recognition module is used to identify the similarity between the spectrum signal read under the current sweep voltage and the preset characteristic spectrum signal to determine whether it is the target spectrum, and determine the locking point when it is determined that the target spectrum exists;

[0022] The voltage locking module is used to parse the corresponding automatic frequency locking parameters based on the locking point determined by the similarity recognition module, and send the automatic frequency locking parameters to the digital PID feedback controller, so as to control the digital PID feedback controller to perform PID control locking on the spectral signal voltage of the locking point as the control quantity based on the current frequency locking parameters.

[0023] Preferably, the automatic frequency locking operation system further comprises a spectrum signal receiving module for receiving a spectrum signal fed back by a digital PID feedback controller under a current frequency sweep voltage.

[0024] Preferably, the automatic frequency locking operation system further comprises a frequency sweeping voltage regulating module for automatically adjusting the frequency sweeping voltage range output by the digital PID feedback controller when it is determined that the target spectrum does not exist under the current frequency sweeping voltage.

[0025] Preferably, the automatic frequency locking operation system further comprises a monitoring module for determining whether it is still in a locked state based on a currently received spectral signal after entering PID locking.

[0026] Preferably, the automatic frequency locking operation system also includes a memory and a sweeping frequency voltage regulation module, the memory is used to store the voltage when the previous locking was successful; the sweeping frequency voltage regulation module is used to determine the sweeping frequency voltage range output by the digital PID feedback controller based on the voltage when the previous locking was successful stored in the memory.

[0027] Preferably, the automatic frequency locking operation system further comprises a mode switching switch, and the mode switching is used to control the automatic frequency locking operation system to switch between an automatic locking mode and a waiting locking mode.

[0028] Since the utility model adopts the above-mentioned scheme, it can automatically modulate the scanning voltage of the laser according to different types of characteristic spectra, realize spectral signal feedback under the corresponding scanning voltage, and thus can perform similarity recognition based on the characteristic spectrum and the feedback spectral signal to determine the target spectrum and the locking point. Therefore, the above-mentioned laser automatic frequency locking system based on similarity recognition spectrum can automatically modulate the scanning voltage of the laser, and can effectively find the characteristic spectrum and locking point even when the laser mode hops or there is large environmental interference, with less interference from the environment and a more stable working state. In addition, since a similarity recognition module is adopted, the characteristic peaks of various spectra including saturated absorption spectra, modulation transfer spectra, frequency modulation spectra, etc. can be intelligently identified, and the application range is wider; and the method of determining the locking point based on similarity recognition can be more

[0029] Quickly determine the locking point and work more efficiently. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the structure of the laser automatic frequency locking system involved in this application;

[0031] Figure 2 It is a schematic diagram of the structure of the spectrum part involved in this application;

[0032] Figure 3 This is a flow chart of the laser automatic frequency locking method involved in this application.

[0033] Reference numerals:

[0034] Laser 1, spectrum module 2, first beam splitter prism 21, second beam splitter prism 22, electro-optic modulator 23, rubidium gas chamber 24, photodiode 25, modulation and demodulation module 26, digital PID feedback controller 3, automatic frequency locking operation system 4. DETAILED DESCRIPTION

[0035] The embodiments of the present utility model are described in detail below.

[0036] Glossary:

[0037] Electro-optic modulator (EOM): An electro-optic modulator is a modulator that uses the electro-optic effect of an electro-optic crystal. The electro-optic effect means that when a voltage is applied to an electro-optic crystal, the refractive index of the electro-optic crystal will change, resulting in a change in the characteristics of the light wave passing through the crystal, thereby modulating the phase, amplitude, intensity and polarization state of the optical signal.

[0038] Laser frequency locking: Using feedback control technology, the output frequency of the laser is compared with the reference frequency, and then the output frequency of the laser is adjusted through feedback control to keep it consistent with the reference frequency.

[0039] Embodiment 1:

[0040] This embodiment provides a laser automatic frequency locking system based on similarity recognition spectrum. Figure 1 As shown, the laser automatic frequency locking system based on similarity recognition spectrum includes a laser 1, a spectrum module 2, a digital PID feedback controller 3 and an automatic frequency locking operation system 4. The output end of the laser 1 is connected to the input end of the spectrum module 2, the output end of the spectrum module 2 is connected to an input end of the digital PID feedback controller 3, an output end of the digital PID feedback controller 3 is connected to the input end of the laser 1, and the digital PID feedback controller 3 interacts with the automatic frequency locking operation system 4.

[0041] The laser 1 includes a laser light source and a laser 1 controller. The laser 1 controller controls the laser light source to output an optical frequency signal to the spectrum module 2 .

[0042] The spectrum module 2 modulates and demodulates the optical frequency signal output by the laser 1 and outputs the spectrum signal to the digital PID feedback controller 3. Figure 2 As shown, the spectrum module 2 includes a fiber collimator head, a first beam splitter prism 21, a second beam splitter prism 22, and an electro-optic modulator 23 (EOM) and a rubidium gas chamber 24 arranged in parallel from the signal input direction to the output direction. The emission end of the second beam splitter prism 22 is connected to the modulation and demodulation module 26 through a photodiode 25. The first output end of the modulation and demodulation module 26 is connected to the photoelectric modulator, and the first output end outputs a radio frequency modulated signal to the photoelectric modulator. The second output end of the modulation and demodulation module 26 is connected to the digital PID feedback controller 3, and the second output end outputs a spectrum signal to the digital PID feedback controller 3.

[0043] The spectrum module 2 realizes the processing of the optical path part and the circuit part. The optical path part is processed as follows: Figure 2 As shown, the spectrum module 2 is connected to the output end of the laser 1 at its optical fiber collimation head. The spectrum module 2 introduces the light source emitted by the laser 1 into the free space through the optical fiber collimation head, and divides the light path into two paths through the first beam splitter prism 21. One path directly enters the rubidium gas chamber 24, and the other path is processed by the electro-optic modulator 23 (EOM). The two light paths are combined in the rubidium gas chamber 24 through the second beam splitter prism 22 to eliminate the Doppler shift. The light beams divided into two paths by the first beam splitter prism 21 are combined in the second beam splitter prism 22, and the combined spectral signals are converted into electrical signals through the photodiode 25 (PD).

[0044] The circuit part is processed as follows: Figure 2 As shown, the spectrum module 2 includes a modulation and demodulation module 26, and the modulation and demodulation module 26 includes an operational amplifier and a demodulation chip. The operational amplifier is used to perform active bandpass filtering and voltage amplification on the corresponding frequency crystal oscillator signal through the operational amplifier. One input end of the modulation and demodulation module 26 is the input end of the external reference signal. The input reference signal is divided into two paths. The first path signal is output to the electro-optical modulator 23 as a signal of the required frequency of the electro-optical modulator 23; the second path signal is used as a reference signal when the modulation and demodulation module 26 demodulates. Specifically, for the electrical signal input to the modulation and demodulation module 26 by the photodiode 25, the demodulation chip demodulates the electrical signal according to the second path signal. The demodulated spectrum signal is output to the digital PID controller.

[0045] The digital PID feedback controller 3 includes a microcontroller (MCU), a digital analog converter (DAC) and an analog-to-digital converter (ADC). The microcontroller is connected to the digital analog converter and the analog-to-digital converter respectively. The output end of the digital analog converter is connected to the laser 1. The microcontroller (MCU) drives the digital analog converter (DAC) to lock the laser 1. The input end of the analog-to-digital converter is connected to the output end of the spectrum. The microcontroller drives the analog-to-digital converter (ADC) at the same time to read the spectrum signal in parallel at high speed, convert the read spectrum signal into a digital signal, and then package the data according to the communication protocol and send it to the automatic frequency locking operation system 4. In the embodiment, a 16-bit analog-to-digital converter is selected to read the spectrum signal. The digital PID controller communicates with the automatic frequency locking operation system 4 via a universal serial bus (USB), and the signal transmission is high-speed and stable. At the same time, the digital PID feedback controller 3 outputs a sweeping signal to the laser 1 according to the currently determined sweeping voltage range.

[0046] The automatic frequency locking operation system 4 includes a spectrum signal receiving module, a spectrum scanning module, a similarity recognition module and a voltage locking module.

[0047] The spectral signal receiving module is used to receive the spectral signal processed by the digital PID feedback controller 3, that is, the digital PID controller described above converts the read spectral signal into a digital signal and packages the data according to the communication protocol. It can be understood that the automatic frequency locking operation system 4 includes a data parsing module, which is used to parse the spectral signal data from the digital PID controller according to the communication protocol, and parse the data for subsequent processing.

[0048] A spectrum scanning module is used to control the digital PID feedback controller 3 to output a frequency sweeping voltage to the laser 1; the frequency sweeping voltage range is preset corresponding to different types of characteristic spectra;

[0049] A similarity recognition module is used to identify the similarity between the spectrum signal read under the current sweep voltage and the preset characteristic spectrum signal, determine whether the target spectrum exists in the spectrum signal, and locate the target spectrum to obtain a locking point when the target spectrum is detected;

[0050] The voltage locking module is used to analyze the corresponding automatic frequency locking parameters based on the locking point determined by the similarity recognition module, and send the automatic frequency locking parameters to the digital PID feedback controller 3, control the digital PID feedback controller 3 to perform PID control and lock the spectral signal voltage of the locking point as the control quantity based on the current frequency locking parameters, and enter the locking state.

[0051] Through the cooperation of the above modules, after the automatic frequency locking operation system 4 obtains the spectrum signal data, it makes a similarity judgment on the signal, and can automatically identify which spectrum segment needs to be locked, and can also identify the locking point and the automatic frequency locking parameters.

[0052] The swept frequency voltage at the locking point and the obtained spectral signal voltage are included, so that the digital PID feedback controller 3 can perform PID control locking on the spectral signal voltage at the locking point as the control quantity.

[0053] As a preferred embodiment, the automatic frequency locking operation system 4 further includes a frequency sweeping voltage adjustment module for automatically adjusting the frequency sweeping voltage range output by the digital PID feedback controller 3 when it is determined that the target spectrum does not exist under the current frequency sweeping voltage.

[0054] As a preferred embodiment, the automatic frequency locking operation system 4 also includes a monitoring module, which is used to determine whether it is still in the locked state based on the currently received spectrum signal after entering the locked state. The monitoring module is set to quickly control the spectrum scanning module to re-scan the frequency after detecting that the laser 1 is unlocked, and determine the sweeping voltage within a preset range of the voltage when the previous locking was successful, so that the automatic frequency locking state can be entered more quickly during the re-locking process.

[0055] The above-mentioned laser automatic frequency locking system based on similarity recognition spectrum can automatically modulate the sweeping voltage of laser 1, and can effectively find characteristic spectrum and locking point even when laser 1 is mode-hopping or the environment is disturbed. It is less affected by the environment and has a more stable working state. In addition, due to the use of similarity recognition module, it can intelligently identify the characteristic peaks of various spectra including saturated absorption spectrum, modulation transfer spectrum, frequency modulation spectrum, etc., and has a wider range of applications; and the method of determining the locking point based on similarity recognition can determine the locking point faster and with higher work efficiency.

[0056] Embodiment 2:

[0057] This embodiment provides a laser automatic frequency locking method based on similarity recognition spectrum, which is run in the laser automatic frequency locking system in embodiment 1. Figure 3 As shown, the method comprises the following steps:

[0058] S1, controls the digital PID feedback controller to output a sweeping voltage to the laser, and the current state is the scanning state;

[0059] S2, obtaining the spectrum signal output by the laser under the current sweep voltage;

[0060] S3, performing similarity recognition between the preset characteristic spectrum and the acquired spectrum signal through a similarity algorithm to determine whether there is a target spectrum in the current spectrum signal. If so, executing step S4; if the target spectrum is not recognized, adjusting the sweep voltage and returning to executing step S1;

[0061] S4, determining a locking point of the current characteristic spectrum based on the peak position of the similarity coefficient;

[0062] S5, after obtaining the locking point, determining the frequency locking parameters of the current characteristic spectrum based on the locking point, controlling the digital PID feedback controller to determine the control amount based on the frequency locking parameters to perform PID control locking, and the current state is the locking state.

[0063] The laser automatic frequency locking method based on similarity recognition spectrum can realize the automatic frequency locking control of the laser through the above steps, and can intelligently identify the characteristic peaks of various spectra including saturation absorption spectrum, modulation transfer spectrum, frequency modulation spectrum, etc. based on the similarity recognition algorithm, and has a wider range of applications; and can automatically identify the required locking point position, the locking point recognition method is simple, and the recognition efficiency is higher. In addition, the above method can automatically adjust the sweep frequency range of the laser, and the method has strong adaptability.

[0064] In the above step S1, after receiving the sweep voltage, the laser can output a corresponding optical frequency signal. The optical frequency signal output by the laser is Figure 1The spectrum part shown and the digital PID feedback controller are processed to obtain the spectrum signal that can be recognized and processed by the automatic frequency locking operation system. The sweeping voltage output by the laser in S1 corresponds to different types of characteristic spectra, such as saturated absorption spectrum, modulation transfer spectrum, frequency modulation spectrum, etc., and the sweeping voltage range that is expected to obtain the corresponding type of characteristic spectrum is preset. Preferably, in the embodiment,

[0065] The scanning state is monitored. If an error occurs during the process of outputting the sweeping voltage to the laser, step S2 is not continued, and a scanning fault prompt is output externally. The scanning state is monitored specifically by monitoring the preset parameters during the process of the laser outputting the sweeping voltage. The specific implementation method is a conventional technical means in the art and is not described in detail here.

[0066] It can be understood by those skilled in the art that, before executing the above step S1, it is necessary to perform parameter initialization settings to set necessary parameters such as PID control coefficient, sweep voltage amplitude, and sweep voltage range.

[0067] What is read in the above step S2 is the spectrum signal corresponding to the optical frequency signal output by the laser after receiving the frequency sweeping voltage. The signal is a voltage signal. The error signal can be determined by combining the spectrum signal and controlled through feedback.

[0068] In the above step S3, adjusting the frequency sweep voltage specifically includes:

[0069] The sweep voltage range is preset corresponding to different types of characteristic spectra, and each sweep voltage range is divided into multiple sweep voltage segments in advance, for example, the first segment is 0.1V~0.3V, and after stepping one segment, it is 0.2V~0.4V... and so on, and multiple sweep voltage segments are divided; if the current sweep voltage segment does not identify the target spectrum, the sweep voltage segment adjacent to the current sweep voltage segment is automatically stepped one segment to select as the sweep voltage and re-execute step S1. For example, by such a setting, the sweep voltage can be automatically adjusted without manual operation, which can reduce manual participation and improve work efficiency. If all the sweep voltage segments within the sweep voltage range corresponding to the current characteristic spectrum are used as the sweep voltage and still cannot identify the target spectrum, it means that the preset sweep voltage range corresponding to the characteristic spectrum is wrong, and the preset sweep voltage range needs to be manually adjusted. For example, if the target spectrum is not found in 0.1V~0.3V, step to 0.2V~0.4V for sweeping.

[0070] The above step S3 specifically includes sliding the preset characteristic spectrum information on the obtained spectrum signal to perform similarity calculation, and obtaining a set of similarity coefficients having a length equal to the sum of the lengths of the two pieces of information (the preset characteristic spectrum information and the spectrum signal read in step S2). In an embodiment, the similarity coefficients and the corresponding sliding positions can be stored in an array, and the spectrum information at the corresponding position of the spectrum signal can be determined based on the sliding position.

[0071] Determine whether the target spectrum appears in the current spectral signal based on the peak value of the similarity coefficient. Specifically, when the target spectrum appears in the obtained spectrum, the similarity coefficient will present a peak at the corresponding sliding position, and judge whether the similarity coefficient peak matches the preset threshold to characterize the existence of the target spectrum. If the similarity coefficient peak matches the preset threshold, it is determined that the target spectrum exists, otherwise the current similarity coefficient peak cannot characterize the existence of the target spectrum. Among them, the preset threshold corresponds to the characteristic spectrum type one by one, and the threshold can be a point value or a range value. In the embodiment, a specific matching rule is preset to determine whether the peak value of the similarity coefficient matches the preset threshold. As an implementable method, the preset threshold is a range value, and as long as the peak value of the similarity coefficient falls within the range value, it is determined that it matches the preset threshold. As another implementable method, the threshold is a point value, and the specific matching rule is that if the peak value of the similarity coefficient is within 10% before and after the threshold, it is determined that it matches the preset threshold.

[0072] In the above step S4, the locking point of the current characteristic spectrum is determined based on the position of the similarity coefficient peak. Specifically, after determining the existence of the target spectrum, the spectrum information at the sliding position corresponding to the similarity coefficient peak on the spectrum signal is the locking point of the current characteristic spectrum. Further, it is also necessary to determine whether the current sliding position is the locking point in combination with the signal power of the spectrum signal. Specifically, the signal power of the spectrum signal at the sliding position corresponding to the similarity coefficient peak (similarity coefficient peak position, target position) is obtained, and it is compared with the power information of the characteristic spectrum currently used.

[0073] A comparison is made. If the difference between the two is within a preset power range, it is considered that the signal power matches the power of the characteristic spectrum, and the current position is the locking point.

[0074] In the embodiment, the similarity algorithm may adopt cosine similarity, Pearson correlation coefficient or other commonly used similarity algorithms. For example, when the Pearson correlation coefficient is used, for the characteristic spectrum X and the obtained spectral signal Y; the characteristic spectrum X is slid on the obtained spectral signal Y line for calculation, and the length of the characteristic spectrum X is taken. For each point: the product of the difference between the average value of X and X and the difference between the average value of Y and Y is summed, first divided by the square of the difference between the average value of X and X, and the square root of each point is taken after the sum is taken, and then divided by the square of the difference between the average value of Y and Y, and the square root of each point is taken after the sum is taken; after calculation, the required similarity coefficient will be obtained; the formula is Signal power is calculated as follows: for the spectrum signal Y, square the difference between Y and the average value of Y, and sum each point; the formula is The above step S3 can be implemented through the above calculation.

[0075] The above step S5 specifically includes that after obtaining the required locking point, the automatic frequency locking operation system sends the automatic frequency locking parameters, including the scanning voltage of the locking point and the obtained spectral signal voltage, to the digital PID feedback controller, and performs PID control locking on the spectral signal voltage of the locking point as the control quantity.

[0076] Preferably, the method further includes the step: S6, after entering the locked state, determining whether it is still in the locked state based on the currently received spectral signal, and the current state is the monitoring state. In the embodiment, the spectral signal is parsed into a voltage signal, and whether the laser frequency is still in the locked state is determined based on the voltage value of the spectral signal. Specifically, when the variance, standard deviation and maximum value of a set of spectral signal voltages are comprehensively judged to be within a preset range, it is considered that the laser frequency is still in the locked state. If it exceeds the preset range, it is considered that the laser is unlocked; if the laser is unlocked, return to execute step S1. This step can realize intelligent monitoring of the locking state and re-lock in time after unlocking.

[0077] Preferably, step S6 also includes recording the spectrum signal voltage in the successful frequency locking state, and when it is determined that the laser is unlocked and returns to step S1, determining the frequency sweep voltage based on the spectrum signal voltage in the successful frequency locking state. In a specific embodiment, when returning to step S1 for rescanning, the frequency sweep voltage is updated to a certain positive or negative range of the spectrum signal voltage when the last automatic frequency locking was successful, so as to enter the frequency locking state faster during the relocking process. Step S6 can realize the automatic relocking function after losing the lock, so that the frequency locking state of the laser is more stable.

[0078] Preferably, the method is executed through state machine control, which can achieve complete automatic frequency locking, saving a lot of manpower and improving the stability when the laser needs to work in a specific frequency scenario.

[0079] Preferably, the system includes an automatic locking mode and a waiting locking mode. The automatic locking mode is used to realize the control of automatic frequency locking of the laser and automatic re-locking after unlocking. The complete method of steps S1-S6 is executed in the automatic locking mode. In the waiting locking mode, the method does not execute steps S5-S6, and whether to execute steps S1-S4 can be determined according to actual needs. In this embodiment, in the waiting locking mode, the automatic frequency locking system only performs voltage scanning in the current range without frequency locking, which is convenient for observing the spectrum. After starting the automatic frequency locking, it jumps to step S1 to restart the automatic frequency locking process. Figure 3 As shown, the method includes, before executing step S5, determining whether the current mode is automatic locking mode, and if so, executing step S5, otherwise not executing step S5. In the monitoring state, if a control signal is received to switch the current automatic locking mode to the waiting locking mode, the digital PID feedback controller is controlled to disengage from the locking control. In a specific embodiment, the mode switching between the automatic locking mode and the waiting locking mode is performed by the working mode control signal. The method can achieve complete automatic frequency locking by controlling the state machine in the automatic frequency locking operation system, saving a lot of manpower and improving the stability in scenarios where the laser needs to work at a specific frequency; by

[0080] The similarity recognition algorithm can intelligently determine the locking point required for the characteristic spectrum line, and the similarity recognition can identify various spectra, which is widely applicable. This method can effectively find the characteristic spectrum and locking point even when the laser mode hops or the environmental interference is large by automatically modulating the sweeping voltage of the laser; it can intelligently monitor the locking state and relock in time after unlocking; the utility model uses the similarity recognition function method, which can intelligently identify the characteristic peaks of various spectra including saturated absorption spectrum, modulation transfer spectrum, frequency modulation spectrum, etc., and has a wide range of applications; it can directly identify the required locking point position and quickly lock; it can intelligently adjust the laser sweeping range and has strong adaptability; it has achieved a fully intelligent laser automatic frequency locking function, which solves a lot of manpower work and meets the needs of various fields for stable laser frequency; it can automatically record the position of the last locking point, effectively reduce the time of re-locking, increase the total time that the laser is in the locked state, and improve work efficiency.

[0081] Although the embodiments of the present invention have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A laser automatic frequency locking system based on similarity recognition spectrum, characterized in that: include: A laser, including a laser light source and a laser controller, wherein the laser controller controls the laser light source to output an optical frequency signal to a spectrum module; A spectrum module, comprising a fiber collimator, a first beam splitter, a second beam splitter, and an electro-optic modulator and a rubidium gas chamber arranged in parallel from the signal input direction to the signal output direction, wherein the emission end of the second beam splitter is connected to the modulation and demodulation module via a photodiode, the first output end of the modulation and demodulation module is connected to the photoelectric modulator, the first output end outputs a radio frequency modulated signal to the photoelectric modulator, the second output end of the modulation and demodulation module is connected to the digital PID feedback controller, and the second output end outputs a spectrum signal to the digital PID feedback controller; A digital PID feedback controller is used to output a frequency sweep signal to the laser, and send a spectrum signal corresponding to the frequency sweep signal to the automatic frequency locking operation system, and at the same time perform PID control and lock the laser based on the automatic frequency locking parameters determined by the automatic frequency locking operation system; The automatic frequency locking operation system is used to determine the locking point of the received spectral signal based on a similarity recognition algorithm, and determine the corresponding automatic frequency locking parameters based on the locking point.

2. The laser automatic frequency locking system based on similarity recognition spectrum according to claim 1, characterized in that: One input end of the modulation and demodulation module is the input end of the external reference signal. The input reference signal is divided into two paths. The first signal is output to the electro-optical modulator as a signal of the required frequency of the electro-optical modulator; the second signal is used as a reference signal when the modulation and demodulation module demodulates.

3. The laser automatic frequency locking system based on similarity recognition spectrum according to claim 2, characterized in that: The modulation and demodulation module includes an operational amplifier and a demodulation chip; the operational amplifier is used to perform active bandpass filtering and voltage amplification on the electrical signal input through the photodiode; the demodulation chip is used to demodulate the electrical signal amplified by the operational amplifier based on the second signal as a reference signal.

4. The laser automatic frequency locking system based on similarity recognition spectrum according to claim 1, characterized in that: The digital PID feedback controller includes a microcontroller, a digital-to-analog converter and an analog-to-digital converter. The microcontroller is connected to the digital-to-analog converter and the analog-to-digital converter respectively. The output end of the digital-to-analog converter is connected to the laser. The microcontroller drives the digital-to-analog converter to lock the frequency of the laser. The input end of the analog-to-digital converter is connected to the output end of the spectrum. The microcontroller drives the analog-to-digital converter to read the spectrum signal in parallel at high speed and convert the read spectrum signal into a digital signal.

5. The laser automatic frequency locking system based on similarity recognition spectrum according to claim 1, characterized in that: The automatic frequency locking operation system includes: The spectrum scanning module is used to control the digital PID feedback controller to output a preset frequency sweep voltage to the laser; A similarity recognition module is used to identify the similarity between the spectrum signal read under the current sweep voltage and the preset characteristic spectrum signal to determine whether it is the target spectrum, and determine the locking point when it is determined that the target spectrum exists; The voltage locking module is used to parse the corresponding automatic frequency locking parameters based on the locking point determined by the similarity recognition module, and send the automatic frequency locking parameters to the digital PID feedback controller, so as to control the digital PID feedback controller to perform PID control locking on the spectral signal voltage of the locking point as the control quantity based on the current frequency locking parameters.

6. The laser automatic frequency locking system based on similarity recognition spectrum according to claim 5, characterized in that: The automatic frequency locking operation system also includes a spectrum signal receiving module for receiving a spectrum signal fed back by a digital PID feedback controller under a current frequency sweep voltage.

7. The laser automatic frequency locking system based on similarity recognition spectrum according to claim 5, characterized in that: The automatic frequency locking operation system also includes a sweeping frequency voltage adjustment module, which is used to automatically adjust the sweeping frequency voltage range output by the digital PID feedback controller when it is determined that there is no target spectrum under the current sweeping frequency voltage.

8. The laser automatic frequency locking system based on similarity recognition spectrum according to claim 5, characterized in that: The automatic frequency locking operation system further includes a monitoring module, which is used to determine whether it is still in a locked state based on a currently received spectrum signal after entering PID locking.

9. The laser automatic frequency locking system based on similarity recognition spectrum according to claim 7, characterized in that: The automatic frequency locking operation system also includes a memory and a sweeping frequency voltage adjustment module, wherein the memory is used to store the voltage when the previous locking was successful; the sweeping frequency voltage adjustment module is used to determine the sweeping frequency voltage range output by the digital PID feedback controller based on the voltage when the previous locking was successful stored in the memory.

10. The laser automatic frequency locking system based on similarity recognition spectrum according to claim 1, characterized in that: The automatic frequency locking operation system further comprises a mode switching switch, and the mode switching is used to control the automatic frequency locking operation system to switch between an automatic locking mode and a waiting locking mode.

Images