Laser Automatic Frequency Stabilization Method, Device and Storage Medium Based on Iodine Molecular Absorption Lines

Abstract

The present invention discloses a laser automatic frequency stabilization method, device and storage medium based on iodine molecular absorption lines. Based on the technical theory of iodine molecular absorption lines, a sweep point-transmittance map is established in the sweep frequency mode, and the frequency stabilization reference point corresponding to the frequency stabilization frequency in the iodine molecular absorption spectrum diagram is found. In the frequency stabilization mode, by comparing the current transmittance with the set target transmittance, the analog voltage of the seed source is automatically adjusted, so as to achieve the stability of the output frequency of the seed source and realize long-term automatic frequency stabilization at low cost.

Description

Technical Field

[0001] The invention relates to the technical field of laser systems, and in particular to a laser automatic frequency stabilization method, device and storage medium based on iodine molecule absorption lines. Background Art

[0002] With the development of laser technology, laser, as one of the important symbols of modern science and technology, has been widely used in many fields, laying the foundation for the development of laser frequency stabilization technology. Laser frequency stabilization technology is an important tool for basic scientific research and a key component of cutting-edge science, playing an increasingly important role in modern science.

[0003] Lasers with long-term frequency stability are crucial in many fields of science and technology. Common frequency stabilization methods include the Lamb Notch frequency stabilization method, the reference cavity frequency locking method, the saturated absorption frequency stabilization technology, etc. Different frequency stabilization methods have their own advantages and disadvantages. For example, the Lamb Notch frequency stabilization method relies on piezoelectric crystals to control the cavity length, which is expensive; the reference cavity frequency locking method can narrow the line width, but it is difficult to overcome long-term frequency drift.

[0004] In the patent number CN104953459A, the name is "A transmission cavity frequency stabilization system for long-term stable laser frequency and

[0005] The patent number CN114142332A and the title “Optical system and laser frequency stabilization device for laser frequency stabilization” provide an optical system and a laser frequency stabilization device for laser frequency stabilization. However, the above two patents have complex structures and high costs, and neither involves long-term automatic frequency stabilization, and cannot make corrections and adjustments in time when the frequency drifts. Summary of the invention

[0006] Technical purpose: In view of the shortcomings of the existing frequency stabilization system, which is complex in structure, high in cost and cannot achieve long-term automatic frequency stabilization, the present invention discloses a low-cost laser automatic frequency stabilization method, device and storage medium based on iodine molecular absorption lines, which can automatically adjust and correct when the frequency drifts to achieve long-term automatic frequency stabilization.

[0007] Technical solution: To achieve the above technical objectives, the present invention adopts the following technical solution:

[0008] The laser automatic frequency stabilization method based on iodine molecule absorption line comprises the following steps:

[0009] S01, firstly output a frequency sweeping voltage to the seed source through the DA module according to the set frequency stabilization frequency, and establish a frequency sweeping point-transmittance spectrum according to the transmittance of the iodine molecule to the laser source corresponding to the frequency sweeping voltage;

[0010] S02. Compare the sweep frequency point - transmittance spectrum with the iodine molecular absorption spectrum line to identify the frequency stabilization reference point corresponding to the set frequency stabilization frequency in the spectrum;

[0011] S03. During frequency stabilization output, the DA module outputs a frequency stabilization voltage to the seed source, performs beam splitting and sampling on the laser source output by the seed source, passes the split light source through the iodine molecular absorption cell, detects the current transmittance, compares the current transmittance with the target transmittance corresponding to the frequency stabilization reference point, and adjusts the output control quantity of the DA module through the PI algorithm according to the comparison result to maintain the frequency stabilization output of the seed source.

[0012] Preferably, in step S02, the process of identifying the frequency stabilization reference point in the spectrum includes:

[0013] S021. The sweep frequency point - transmittance spectrum is filtered using the sliding window averaging method, and the number of sliding windows is 3. The filtered data where x n-1 、x n 、x n+1 are the original data;

[0014] S022. For the filtered data, calculate the amplitude and slope values of each peak and valley, as well as the amplitude difference between adjacent peaks and valleys, and use the calculated data as the eigenvalue set;

[0015] S023. Similarly calculate the amplitude and slope values of each peak and valley, as well as the amplitude difference between adjacent peaks and valleys for the data corresponding to the iodine molecular absorption spectrum line, and use the calculated data as the second eigenvalue set;

[0016] S024. Compare the data in the eigenvalue set with the data in the second eigenvalue set to obtain the iodine molecular absorption spectrum line corresponding to the sweep frequency point - transmittance spectrum.

[0017] Preferably, in step S03, the process of stabilizing the frequency of the laser output by the seed source includes:

[0018] S031. Confirm the corresponding target transmittance in the iodine molecular absorption spectrum line according to the set frequency stabilization frequency, and confirm the sweep frequency point corresponding to the edge line in the sweep frequency point - transmittance spectrum, and use this sweep frequency point as the starting point of frequency stabilization;

[0019] S032. During the frequency stabilization control process, the current transmittance of the iodine molecular absorption cell will change. Calculate the difference between the current transmittance and the target transmittance, and calculate the output voltage u(k) of the DA module;

[0020]

[0021] where e(k) is the error (target transmittance - current transmittance) when collected, K pis the proportionality coefficient, Ki is the integral coefficient, u(k) is the calculated regulated voltage value, and the output feedback regulated voltage is used to control the current transmittance to be stabilized at the target transmittance;

[0022] S033. When the lock is lost during the frequency stabilization process, the current transmittance will deviate significantly from the target transmittance. At this time, when the PC detects the system lock loss, it will automatically perform secondary frequency sweeping and frequency stabilization.

[0023] Preferably, the process of calculating the transmittance includes: according to the range of the frequency stabilization frequency, the split light source is used with the frequency doubling method to make the wavelength range of the frequency-doubled light source fall within the iodine molecule absorption range, and then the light beam is output to the iodine molecule absorption cell and the optical power detection board through a 1:1 beam splitter, and the optical power of the transmitted light after passing through the iodine molecule absorption cell and the power value of the reference light without passing through the iodine molecule absorption cell are detected to calculate the transmittance.

[0024] The present invention also provides a frequency stabilization device using the above laser automatic frequency stabilization method based on iodine molecular absorption lines, including a seed source, an optical fiber beam splitter, a continuous fiber amplifier, a PPLN frequency doubling crystal, an iodine molecule absorption cell, an optical power detection board, a frequency stabilization data acquisition card, and a PC;

[0025] The seed source outputs tunable continuous seed light near the frequency stabilization frequency to the optical fiber beam splitter;

[0026] The optical fiber beam splitter divides the seed light into two paths, one path is output to the continuous fiber amplifier, and the other path is output to the PPLN frequency doubling crystal;

[0027] The PPLN frequency doubling crystal performs frequency doubling processing on the received light beam to make the wavelength fall within the iodine molecule absorption range; and through the beam splitter and total reflection mirror at the outlet end, the frequency-doubled light beam is respectively transmitted to the iodine molecule absorption cell and the optical power detection board;

[0028] The iodine molecule absorption cell absorbs the split light beam and transmits the transmitted light to another optical power detection board;

[0029] The optical power detection board converts the reference light and the transmitted light into voltage signals through a photodiode and transmits them to the frequency stabilization data acquisition card;

[0030] The frequency stabilization data acquisition card transmits the voltage data to the PC and adjusts the output frequency of the seed source according to the instructions of the PC.

[0031] Preferably, the seed source adjusts the analog voltage through a DA module to control the seed current and change the output wavelength.

[0032] Preferably, the optical fiber beam splitter is a 1×2 optical fiber beam splitter, and the splitting ratio is 1∶9, 90% is transmitted to the continuous fiber amplifier, and 10% is transmitted to the PPLN frequency doubling crystal.

[0033] Preferably, the beam splitting ratio of the beam splitter is 1:1, splitting the light into two beams. One beam directly reaches the optical power detection board as the reference light for calculating the transmittance, and the other beam is incident on the iodine molecular absorption cell through a total reflection mirror as the transmitted light, and then received by another optical power detection board.

[0034] The present invention also provides a storage medium storing computer-executable instructions, and the instructions are used to implement the above frequency stabilization method when executed by a processing unit.

[0035] Beneficial effects: Based on the technical theory of iodine molecular absorption lines, the present invention proposes a laser automatic frequency stabilization device based on iodine molecular absorption lines. By comparing the current transmittance with the set target transmittance, the analog voltage of the seed source is automatically adjusted, so as to keep the output frequency of the seed source stable and achieve low-cost long-term automatic frequency stabilization. Description of the Drawings

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art.

[0037] Figure 1 It is the overall flowchart of the laser automatic frequency stabilization method of the present invention;

[0038] Figure 2 It is the flowchart of the frequency sweeping process of the laser automatic frequency stabilization method of the present invention;

[0039] Figure 3 It is the flowchart of the frequency stabilization process of the laser automatic frequency stabilization method of the present invention;

[0040] Figure 4 It is the iodine molecular absorption spectrum diagram of the present invention;

[0041] Figure 5 It is the frequency sweeping point-transmittance spectrum diagram of the present invention;

[0042] Figure 6 It is the structural schematic diagram of the laser automatic frequency stabilization device of the present invention;

[0043] Among them, 1-seed source, 2-optical fiber beam splitter, 3-continuous fiber amplifier, 4-PPLN frequency doubling crystal, 5-iodine molecular absorption cell, 6-optical power detection board, 7-frequency stabilization data acquisition card, 8-PC, 9-beam splitter, 10-total reflection mirror. Specific Embodiments

[0044] The following will more clearly and completely illustrate the present invention by way of a preferred embodiment in conjunction with the drawings, but the present invention is not limited to the scope of the described embodiments.

[0045] Such as Figures 1 - 3The following shows the laser automatic frequency stabilization method based on the iodine molecular absorption line disclosed by the present invention. S01. First, according to the set frequency stabilization frequency, a frequency-sweeping voltage is output to the seed source through the DA module, and a frequency-sweeping point-transmittance map is established based on the transmittance of iodine molecules to the laser source corresponding to the frequency-sweeping voltage. The process of calculating the transmittance includes: according to the range of the frequency stabilization frequency, the split light source uses the frequency doubling method to make the wavelength range of the frequency-doubled light source fall within the iodine molecular absorption range, and then the light beam is output to the iodine molecular absorption cell and the optical power detection board through a 1:1 beam splitter, and the optical power of the transmitted light after passing through the iodine molecular absorption cell and the power value of the reference light without passing through the iodine molecular absorption cell are detected, and the transmittance is calculated.

[0046] S02. Compare the frequency-sweeping point-transmittance map with the iodine molecular absorption spectrum line to identify the frequency stabilization reference point corresponding to the set frequency stabilization frequency in the map;

[0047] In step S02, the process of identifying the frequency stabilization reference point in the map includes:

[0048] S021. The frequency-sweeping point-transmittance map is filtered using the sliding window averaging method, and the number of sliding windows is 3. The filtered data where x n-1 、x n 、x n+1 are the original data;

[0049] S022. For the filtered data, find the amplitude and slope values of each peak and valley, and the amplitude difference between adjacent peaks and valleys, and use the calculated data as the eigenvalue set;

[0050] S023. Similarly calculate the amplitude and slope values of each peak and valley, and the amplitude difference between adjacent peaks and valleys for the data corresponding to the iodine molecular absorption spectrum line, and use the calculated data as the second eigenvalue set;

[0051] S024. Compare the data in the eigenvalue set with the data in the second eigenvalue set to obtain the iodine molecular absorption spectrum line corresponding to the frequency-sweeping point-transmittance map.

[0052] S03. During frequency stabilization output, the DA module outputs a frequency stabilization voltage to the seed source, splits and samples the laser source output by the seed source, passes the split light source through the iodine molecular absorption cell, detects the current transmittance, compares the current transmittance with the target transmittance corresponding to the frequency stabilization reference point, and adjusts the output control quantity of the DA module through the PI algorithm according to the comparison result to maintain the frequency stabilization output of the seed source.

[0053] In step S03, the process of stabilizing and adjusting the laser frequency output by the seed source includes:

[0054] S031. Confirm the corresponding target transmittance in the iodine molecular absorption line according to the set frequency stabilization frequency, and confirm the frequency sweep points corresponding to the side lines in the frequency sweep point - transmittance spectrogram, and use this frequency sweep point as the starting point of frequency stabilization;

[0055] S032. During the frequency stabilization control process, when the current transmittance of the iodine molecular absorption cell changes, calculate the difference between the current transmittance and the target transmittance, and calculate the output voltage u(k) of the DA module;

[0056]

[0057] Among them, e(k) is the error (target transmittance - current transmittance) when collected, K p is the proportionality coefficient, Ki is the integral coefficient, u(k) is the calculated regulation voltage value, output the feedback regulation voltage, and control the current transmittance to be stable at the target transmittance;

[0058] S033. When loss of lock occurs during the frequency stabilization process, the current transmittance will differ greatly from the target transmittance. At this time, when the PC detects system loss of lock, it will automatically perform secondary frequency sweep and frequency stabilization.

[0059] Such as Figure 6 shown is the laser automatic frequency stabilization device based on the iodine molecular absorption line provided by the present invention. The above frequency stabilization method is used for laser automatic frequency stabilization, including a seed source 1, an optical fiber beam splitter 2, a continuous optical fiber amplifier 3, a PPLN frequency doubling crystal 4, an iodine molecular absorption cell 5, an optical power detection board 6, a frequency stabilization data acquisition card 7, and a PC 8; the seed source 1 outputs tunable continuous seed light near the frequency stabilization frequency to the optical fiber beam splitter 2; the optical fiber beam splitter 2 divides the seed light into two paths, one path is output to the continuous optical fiber amplifier 3, and the other path is output to the PPLN frequency doubling crystal 4; the PPLN frequency doubling crystal 4 performs frequency doubling processing on the received light beam to make the wavelength within the iodine molecular absorption range; and by the beam splitter 9 and the total reflection mirror 10 at the outlet end, the frequency doubled light beam is respectively transmitted to the iodine molecular absorption cell 5 and the optical power detection board 6; the iodine molecular absorption cell 5 absorbs the split light beam and transmits the transmitted light to another optical power detection board 6; the optical power detection board 6 converts the reference light and the transmitted light into voltage signals through a photodiode and transmits them to the frequency stabilization data acquisition card 7; the frequency stabilization data acquisition card 7 transmits the voltage data to the PC 8, and the PC stores computer - executable instructions. The frequency stabilization data acquisition card 7 adjusts the output frequency of the seed source 1 according to the instructions of the PC 8.

[0060] Specifically, the seed source 1 of the present invention adjusts the analog voltage through the DA module, controls the seed current, and changes the output wavelength. The DA module is electrically connected to the frequency stabilization data acquisition card 7, and the analog voltage of the DA module is controlled through the frequency stabilization data acquisition card 7. The optical fiber splitter 2 is a 1×2 optical fiber splitter, and the splitting ratio is 1∶9. 90% is transmitted to the continuous fiber amplifier 3, and 10% is transmitted to the PPLN frequency doubling crystal 4. The beam splitter 9 has a splitting ratio of 1∶1, ensuring that the powers of the two split beams are the same, facilitating subsequent transmittance detection and reducing the calculation difficulty; the light is split into two beams, one beam directly reaches the optical power detection board 6 as the reference light for calculating the transmittance, and the other beam is incident on the iodine molecular absorption cell 5 through the total reflection mirror 10 as the transmitted light, and is then received by another optical power detection board 6.

[0061] When the laser automatic frequency stabilization device based on the iodine molecular absorption line provided by the present invention is in use, taking the light source with an output wavelength of 1064 nm as an example, the PC 8 issues a frequency sweep command, and the system starts the frequency sweep mode as Figure 2 shown. The frequency stabilization data acquisition card 7 first calculates the frequency sweep voltage value, outputs the frequency sweep voltage to the DFB 1064 nm seed source through the DA module, and realizes the change of the frequency of the seed source from small to large in the 1064 nm range. The two optical power detection boards respectively detect the optical power of the reference light and the transmitted light, and input the detected optical voltage signals into the frequency stabilization data acquisition card, which is uploaded to the PC by the frequency stabilization data acquisition card, generating a frequency sweep point - transmittance map as Figure 5 shown. The abscissa frequency sweep point corresponds to a frequency sweep voltage, which corresponds to the output wavelength of the seed source, and the ordinate represents the transmittance of the iodine molecular absorption cell. Since the transmittance of iodine molecules to different wavelengths is different, the frequency stabilization reference point of the set frequency stabilization frequency in the frequency sweep point - transmittance map can be confirmed through the absorption spectrum line of iodine molecules.

[0062] Then, the frequency sweep point corresponding to the frequency stabilization reference point is used as the starting point of the frequency stabilization mode and is issued to the frequency stabilization data acquisition card, and the frequency sweep mode is switched to as Figure 3In the frequency stabilization mode shown, the seed source starts to output frequency-stabilized light. The DFB 1064nm seed source outputs tunable continuous seed light near 1064nm. After passing through a 1×2 fiber splitter, 90% of the seed light passes through a continuous fiber amplifier and outputs 300mW of laser light. The other 10% of the seed light is frequency-doubled to 532nm by a PPLN frequency-doubling crystal, and then passes through a 1:1 beam splitter and a total reflection mirror, and is respectively output to an iodine molecular absorption cell and a light power detection board. The light passing through the iodine molecular absorption cell is output to another light power detection board. The two light power detection boards send the detected data to the PC through a frequency stabilization data acquisition card, calculate the transmittance, and compare the current transmittance with the target transmittance at the frequency stabilization reference point. According to the PI algorithm, the output control quantity of the DA module is obtained, and the DA output control quantity is given to the DFB 1064nm seed source to realize the adjustment of the frequency of the seed source near the frequency stabilization point. If the current transmittance differs greatly from the target transmittance, at this time the PC detects that the system is unlocked and will automatically perform secondary frequency sweeping and frequency stabilization.

[0063] If the locked frequency is set to 532.2599nm, corresponding to Figure 4 the 1109 side line in the iodine molecular absorption spectrum diagram shown, in Figure 5 the frequency sweep point - transmittance spectrum diagram, the algorithm identifies the frequency sweep point consistent with the 1109 side line as x = 534. This point is used as the starting point of the frequency stabilization mode. The PC issues the frequency stabilization starting point 534 and switches the working mode of the frequency stabilization data acquisition card to the frequency stabilization mode. The frequency stabilization data acquisition card will perform frequency stabilization work around the frequency sweep voltage corresponding to the 534 point, enabling the system to complete the automatic frequency stabilization function.

[0064] The above is only the preferred implementation mode of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A laser automatic frequency stabilization method based on the absorption line of iodine molecules, characterized in that Including the steps: S01. First, according to the set frequency stabilization frequency, output a frequency-sweeping voltage to the seed source through the DA module, and establish a frequency-sweeping point-transmittance map based on the transmittance of iodine molecules to the laser source corresponding to the frequency-sweeping voltage; S02. Compare the frequency-sweeping point-transmittance map with the iodine molecular absorption spectrum line to identify the frequency stabilization reference point corresponding to the set frequency stabilization frequency in the map; S03. During frequency stabilization output, the DA module outputs a frequency stabilization voltage to the seed source, performs beam splitting and sampling on the laser source output by the seed source, passes the split light source through the iodine molecular absorption cell, detects the current transmittance, compares the current transmittance with the target transmittance corresponding to the frequency stabilization reference point, and adjusts the output control quantity of the DA module through the PI algorithm according to the comparison result to maintain the frequency stabilization output of the seed source; In step S02, the process of identifying the frequency stabilization reference point in the map includes: S021. The sweep frequency point - transmittance spectrum is filtered using the sliding window averaging method. The number of sliding windows is 3, and the filtered data , where is the original data; S022. Calculate the amplitude, slope value of each peak and valley, and the amplitude difference between adjacent peaks and valleys for the filtered data, and use the calculated data as a set of eigenvalue; S023. Similarly calculate the amplitude, slope value of each peak and valley, and the amplitude difference between adjacent peaks and valleys for the data corresponding to the iodine molecular absorption spectrum line, and use the calculated data as a second set of eigenvalue; S024. Compare the data of the set of eigenvalue with the data of the second set of eigenvalue to obtain the iodine molecular absorption spectrum line corresponding to the frequency-sweeping point-transmittance map; In step S03, the process of performing frequency stabilization adjustment on the laser frequency output by the seed source includes: S031. Confirm the corresponding target transmittance in the iodine molecular absorption spectrum line according to the set frequency stabilization frequency, and confirm the frequency-sweeping point corresponding to the side line in the frequency-sweeping point-transmittance spectrum diagram, and use this frequency-sweeping point as the starting point of frequency stabilization; S032. During the frequency stabilization control process, the current transmittance of the iodine molecular absorption cell changes. Calculate the difference between the current transmittance and the target transmittance, and calculate the output voltage of the DA module. ; ； Among them, is the currently collected error, = target transmittance - current transmittance, is the proportionality coefficient, is the integral coefficient, u(k) is the calculated regulation voltage value, output the feedback regulation voltage, and control the current transmittance to be stable at the target transmittance; S033. When unlocking occurs during the frequency stabilization process, the current transmittance will differ greatly from the target transmittance. At this time, when the PC detects that the system is unlocked, it will automatically perform secondary frequency sweeping and frequency stabilization; The process of calculating the transmittance includes: according to the range of the frequency stabilization frequency, use the frequency doubling method for the split light source to make the wavelength range of the frequency-doubled light source within the iodine molecular absorption range, and then output the light beam to the iodine molecular absorption cell and the optical power detection board through a 1:1 beam splitter, detect the optical power of the transmitted light after passing through the iodine molecular absorption cell and the power value of the reference light without passing through the iodine molecular absorption cell, and calculate the transmittance.

2. The laser automatic frequency stabilization device based on the iodine molecule absorption line uses the laser automatic frequency stabilization method described in claim 1, and is characterized in that, Including a seed source (1), an optical fiber beam splitter (2), a continuous fiber amplifier (3), a PPLN frequency doubling crystal (4), an iodine molecular absorption cell (5), an optical power detection board (6), a frequency stabilization data acquisition card (7), and a PC (8); The seed source (1) outputs adjustable continuous seed light near the frequency stabilization frequency to the optical fiber beam splitter (2); The optical fiber beam splitter (2) splits the seed light into two paths, one path is output to the continuous fiber amplifier (3), and the other path is output to the PPLN frequency doubling crystal (4); The PPLN frequency doubling crystal (4) performs frequency doubling processing on the received light beam to make the wavelength within the iodine molecular absorption range; and is transmitted to the iodine molecular absorption cell (5) and the optical power detection board (6) respectively by the beam splitter (9) and the total reflection mirror (10) at the outlet end; An iodine molecule absorption cell (5) that absorbs the light beam of spectroscopy and transmits the transmitted light to another optical power detection board (6); An optical power detection board (6) that converts the reference light and the transmitted light into voltage signals through a photodiode and transmits them to a frequency stabilization data acquisition card (7); A frequency stabilization data acquisition card (7) that transmits voltage data to a PC (8) and adjusts the output frequency of the seed source (1) according to the instructions of the PC (8).

3. The laser automatic frequency stabilization device based on the iodine molecule absorption line according to claim 2, wherein The seed source (1) adjusts the analog voltage through a DA module, controls the seed current, and changes the output wavelength.

4. The laser automatic frequency stabilization device based on the iodine molecule absorption line according to claim 2, wherein, The optical fiber splitter (2) is a 1×2 optical fiber splitter, and the splitting ratio is 1:

9. 90% is transmitted to the continuous fiber amplifier (3), and 10% is transmitted to the PPLN frequency doubling crystal (4).

5. The laser automatic frequency stabilization device based on the iodine molecule absorption line according to claim 2, characterized in that, The beam splitter (9) has a beam splitting ratio of 1:1, splits the light into two beams. One beam directly reaches the optical power detection board (6) as the reference light for calculating the transmittance, and the other beam is incident on the iodine molecule absorption cell (5) through a total reflection mirror (10) as the transmitted light, and then is received by another optical power detection board (6).

6. A storage medium stores computer-executable instructions, characterized in that: The instruction is used to implement the method described in claim 1 when executed by a processing unit.

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