A method for automatic frequency stabilization of polarization spectrum based on dynamic time planning adjustment algorithm

Abstract

The present invention discloses a polarization spectrum automatic frequency stabilization method based on a dynamic time planning adjustment algorithm, which is characterized in that the polarization spectrum curve is collected to obtain sample data, and the DTW algorithm threshold is set; the FPGA generates a triangle wave and a DC level of a certain amplitude and frequency to scan the PZT; during the scanning process, the current polarization spectrum curve is compared with the sample data to determine whether the DTW algorithm result is lower than the threshold; when it is lower than the threshold, the current triangle wave and DC level state are maintained, and when it is higher than the threshold, the DC level is continuously increased to repeat the previous step; the midpoint position of the edge to be locked of the current frequency discrimination curve is read, and the DC level is changed to adjust to the midpoint of the scanning signal corresponding to the midpoint position of the locking edge; the triangle wave access feedback signal is removed to complete the frequency locking. Compared with the prior art, the present invention enables the system to achieve frequency stabilization in a short time, and provides a stable frequency-stabilized laser light source for devices such as laser interferometers.

Description

Technical Field

[0001] The invention relates to the technical field of laser frequency stabilization, in particular to a polarization spectrum automatic frequency stabilization method based on a dynamic time planning adjustment algorithm. Background Art

[0002] The stability of laser frequency is crucial in the fields of quantum metrology, cold atomic physics, optical fiber communication, laser precision measurement, etc. Semiconductor lasers have the advantages of small size, low cost and easy tuning, which make them suitable for applications in many fields. However, problems such as continuous locking time length and frequency drift of semiconductor lasers affect their application scope. In order to solve this problem, manual stabilization of the wavelength of external cavity semiconductor lasers is currently used, and polarization spectrum stabilization of external cavity semiconductor lasers is performed.

[0003] The frequency stabilization device of the prior art may cause the laser to lose lock due to external interference during operation, and manual frequency stabilization will take a long time, which is not conducive to the use of frequency-stabilized lasers in practical applications. Summary of the invention

[0004] The purpose of the present invention is to design a polarization spectrum automatic frequency stabilization method based on a dynamic time planning adjustment algorithm in view of the deficiencies of the prior art. The DTW algorithm is used to set a threshold for a collected polarization spectrum curve, and a field programmable logic gate array circuit (FPGA) is used to generate a triangular wave and a DC level with a certain amplitude and frequency to scan the piezoelectric ceramic (PZT) of an external cavity semiconductor laser. During the scanning process, the current polarization spectrum curve is compared with sample data to determine whether the DTW algorithm result is lower than the threshold. If it is lower than the threshold, the current triangular wave and DC level state are maintained, and if it is higher than the threshold, the DC level is continuously increased to repeat the previous step; the midpoint position of the edge to be locked of the current frequency discrimination curve is read, the DC level is changed to adjust to the midpoint of the scanning signal corresponding to the midpoint position of the locking edge, the triangular wave access feedback signal is removed, and the frequency locking is completed. The method can monitor and control the frequency state of the laser, and quickly stabilize the frequency again when the laser is unlocked, thereby improving the stability of the system. The present invention solves the problem of automatic frequency stabilization of the polarization spectrum of an external cavity semiconductor laser by using the DTW algorithm, so that the system can achieve frequency stabilization in a short time, and provides a stable frequency-stabilized laser light source for devices such as laser interferometers, and better solves the problem that manual stabilization of the wavelength of an external cavity semiconductor laser is not conducive to the integrated application of semiconductor lasers, and has broad application prospects.

[0005] The object of the present invention is achieved by: a polarization spectrum automatic frequency stabilization method based on DTW algorithm, which is characterized in that the method specifically comprises the following steps:

[0006] Step 1: Collect polarization spectrum curve to obtain sample data and set the DTW algorithm threshold;

[0007] Step 2, a field programmable gate array circuit (FPGA) generates a triangular wave and a DC level of a certain amplitude and frequency to scan the piezoelectric ceramic (PZT) of the external cavity semiconductor laser;

[0008] Step 3: During the scanning process, the current polarization spectrum curve is compared with the sample data to determine whether the DTW algorithm result is lower than the threshold;

[0009] Step 4: When the current triangle wave and DC level are below the threshold, the current triangle wave and DC level are maintained; when the current triangle wave and DC level are above the threshold, the current triangle wave and DC level are returned to step 3.

[0010] Step 5, read the position of the edge to be locked on the current frequency discrimination curve, and change the DC level to adjust it so that the midpoint of the scanning signal corresponds to the midpoint of the locking edge;

[0011] Step 6: Remove the triangular wave access feedback signal to complete frequency locking;

[0012] Furthermore, the setting of the DTW algorithm threshold specifically includes:

[0013] Step 1.1: Collect multiple different polarization spectrum curves, select the target polarization spectrum curve from them, and compare the target spectrum curve with the other polarization spectrum curves using the DTW algorithm;

[0014] Step 1.2: Calculate the cumulative distance matrix between the target spectral curve and the remaining spectral curves one by one during comparison. The zeroth row of the matrix is ​​the target spectral curve, the zeroth column is the remaining spectral curves, the calculation method of the first row and nth column elements is: D[1,n]=|D[0,n]-D[1,0]|+D[1,n-1], the calculation method of the first row and first column elements is: D[n,1]=|D[n,0]-D[0,1]|+D[n-1,1], and the calculation method of the remaining pth row and qth column elements is: D[p,q]= |D[0,q]-D[p,0]|+min(D[p-1,q],D[p,q-1],D[p-1,q-1]);

[0015] Step 1.3, after calculating the cumulative distance matrix, read the value in the last row and last column of the matrix as the result of the DTW algorithm;

[0016] Step 1.4: Compare the DTW algorithm results of different polarization spectrum curves with the target curve.

[0017] The DTW algorithm result of the curve similarity curve is used as the DTW algorithm threshold.

[0018] Furthermore, the specific steps of making the midpoint of the scanning signal correspond to the midpoint of the locking edge include:

[0019] Step 5.1: Read the time a corresponding to the midpoint position of the current locking edge and the time b corresponding to the midpoint value of the rising edge of the triangle wave;

[0020] Step 5.2: Determine whether a and b are equal. If a is greater than b, increase the DC level; if a is less than b, decrease the DC level; if a=b, keep the current DC level unchanged.

[0021] Furthermore, the specific steps of removing the triangular wave access feedback signal to complete the locking correspondence include:

[0022] Step 6.1, each time the triangle wave is reduced by a certain amplitude, and the midpoint of the scanning signal is adjusted to correspond to the midpoint of the locking edge according to step 5, until the triangle wave signal is reduced to 0;

[0023] Step 6.2: Access the feedback signal to complete frequency locking.

[0024] Furthermore, in step 2, the FPGA generates a triangle wave and a DC level signal by a DA circuit.

[0025] Furthermore, during scanning in step 3, the current polarization spectrum curve is collected each time the minimum step of the scanning signal is increased, and the DTW algorithm is compared with the target polarization spectrum curve in step 1.1 to read the last value of the cumulative distance matrix.

[0026] Furthermore, in step 4, if the final value obtained in step 3 is less than the threshold in step 1.4, it is considered that the current polarization spectrum curve is very similar to the target polarization spectrum curve, which means that the scanning signal has scanned to the required spectral line position. If the final value obtained in step 3 is greater than the threshold in step 1.4, step 3 is repeated until a spectrum curve less than the threshold is obtained.

[0027] Compared with the prior art, the present invention has the following beneficial technical effects and significant technical progress:

[0028] 1) Solved the problem that manual frequency stabilization of external cavity semiconductor lasers is not conducive to integrated and automated applications.

[0029] Semiconductor lasers are small in size, low in cost, and have broad application prospects. The stability of laser frequency also plays an important role in laser precision measurement, quantum metrology, optical fiber communication and other fields.

[0030] 2) The DTW algorithm is based on the idea of ​​dynamic programming and is a method for measuring the similarity of two time series. It can determine whether two time series represent the same time series. The present invention applies this algorithm to determine whether the current polarization spectrum scanning position is the specified position. It does not require any complex mathematical calculations and judgment statements. Only simple calculations are needed to obtain the cumulative distance matrix and similarity index. This fully automated frequency stabilization method expands the application prospects of laser interferometers. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a flow chart of the present invention;

[0032] Figure 2 Calculate the cumulative distance matrix flow chart for the DTW algorithm;

[0033] Figure 3 It is a triangle wave scanning signal and polarization spectrum diagram;

[0034] Figure 4 This is a frequency jitter diagram. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] Example 1

[0037] See also Figure 1 The present invention performs automatic polarization spectrum frequency stabilization based on DTW algorithm according to the following steps:

[0038] Step 1: Collect polarization spectrum curve to obtain sample data and set the DTW algorithm threshold.

[0039] Step 1.1: Collect Figure 3 The polarization spectrum curves at multiple different positions such as a, b, and c are shown, among which the target polarization spectrum curve b to be locked is selected, and the target spectrum curve is compared with the remaining polarization spectrum curves by DTW algorithm.

[0040] Step 1.2: Calculate the cumulative distance matrix between the target spectral curve and the other spectral curves one by one during comparison.

[0041] See also Figure 2The zeroth row of the matrix is ​​the voltage value of the target curve, the zeroth column is the voltage values ​​of the remaining spectrum curves, the calculation method of the first row and nth column elements is: D[1,n]=|D[0,n]-D[1,0]|+D[1,n-1], the calculation method of the nth row and 1st column elements is: D[n,1]=|D[n,0]-D[0,1]|+D[n-1,1], and the calculation method of the remaining pth row and qth column elements is: D[p,q]= |D[0,q]-D[p,0]|+min(D[p-1,q],D[p,q-1],D[p-1,q-1]).

[0042] Step 1.3: After calculating the cumulative distance matrix, read the last bit value in the matrix as the result of the DTW algorithm.

[0043] Step 1.4: Compare the DTW algorithm results of different polarization spectrum curves with the target curve, and use the last bit value of the curve similar to the target curve as the DTW algorithm threshold.

[0044] Step 2: FPGA generates a triangle wave with a certain amplitude and frequency and a DC level to scan the PZT of the external cavity semiconductor laser.

[0045] Step 3: See Figure 3 During the scanning process, multiple spectral curves such as a, b, and c in the figure will appear in the scanning window in sequence. The FPGA uses the DTW algorithm to automatically calculate the DTW value of the spectral curve in the current window and the target spectral curve and judge the relationship between the value and the threshold described in step 1.4. The relationship between the DTW algorithm result and the threshold is judged as follows:

[0046] During scanning, the current polarization spectrum curve is collected each time the minimum step of the scanning signal is increased, and the DTW algorithm is used to compare it with the target polarization spectrum curve in step 1.1. The last value of the cumulative distance matrix is ​​read as a similarity index and compared with the threshold.

[0047] Step 4: When the current triangle wave and DC level are maintained below the threshold, return to step 3 when the current triangle wave and DC level are maintained above the threshold. The threshold and similarity index are judged as follows:

[0048] If the final value obtained in step 3 is less than the threshold in step 1.4, it is considered that the current polarization spectrum curve is very similar to the target polarization spectrum curve, which means that the scanning signal has scanned to the required spectral line position. If the final value obtained in step 3 is greater than the threshold in step 1.4, repeat step 3 until a spectrum curve less than the threshold is obtained.

[0049] Step 5. Read the position of the edge to be locked on the current frequency discrimination curve, and change the DC level to adjust the midpoint of the scan signal to correspond to the midpoint of the edge to be locked. The method for corresponding the midpoint of the scan signal to the midpoint of the locked edge is as follows:

[0050] Step 5.1, read the time a corresponding to the midpoint position of the current locking edge and the time b corresponding to the midpoint value of the rising edge of the triangle wave;

[0051] Step 5.2, determine whether a and b are equal, if a is greater than b, increase the DC level, if a is less than b, decrease the DC level;

[0052] Step 5.3: If a=b, keep the current DC level unchanged.

[0053] Step 6: Remove the triangular wave access feedback signal to complete frequency locking. The corresponding method for removing the triangular wave access feedback signal to complete locking is as follows:

[0054] Step 6.1, each time the triangle wave is reduced by a certain amplitude, and the midpoint of the scanning signal is adjusted to correspond to the midpoint of the locking edge according to step 5, until the triangle wave signal is reduced to 0;

[0055] Step 6.2: Access the feedback signal to complete frequency locking.

[0056] In order to illustrate the effectiveness of the present invention, an automatic frequency stabilization system for polarization spectrum of rubidium atoms based on DTW algorithm was established.

[0057] See also Figure 4 , the frequency jitter is 385.5kHz within 40 minutes. Compared with the traditional manual frequency stabilization, the present invention effectively reduces the time required for frequency stabilization. In terms of algorithm complexity, the DTW algorithm does not require any complex mathematical calculations and judgment statements. It only needs to calculate the cumulative distance matrix to obtain the similarity index. The present invention lays the foundation for the application of fully automatic laser interferometers.

[0058] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A polarization spectrum automatic frequency stabilization method based on a dynamic time planning adjustment algorithm, characterized in that: The method specifically comprises the following steps: Step 1: Collect polarization spectrum curve to obtain sample data and set the DTW algorithm threshold; Step 2: Use a field programmable logic gate array circuit to generate a triangular wave of a certain amplitude and frequency and a DC level to scan the piezoelectric ceramic of the external cavity semiconductor laser; Step 3: During the scanning process, the current polarization spectrum curve is compared with the sample data, and it is determined whether the DTW algorithm result is lower than the threshold; Step 4: When it is lower than the threshold, keep the current triangle wave and DC level state, and when it is higher than the threshold, return to step 3; Step 5: Read the position of the edge to be locked on the current frequency discrimination curve, and change the DC level to adjust it so that the midpoint of the scanning signal corresponds to the midpoint of the locked edge; Step 6: Remove the triangle wave feedback signal to complete frequency locking and realize automatic frequency stabilization of polarization spectrum.

2. The polarization spectrum automatic frequency stabilization method based on dynamic time planning adjustment algorithm according to claim 1 is characterized in that: The setting of the DTW algorithm threshold specifically includes: Step 1.1: Collect multiple different polarization spectrum curves, select a target polarization spectrum curve from them, and compare the target spectrum curve with the remaining polarization spectrum curves using a DTW algorithm; Step 1.2: When comparing, calculate the cumulative distance matrix between the target spectral curve and the other spectral curves one by one. The zeroth row of the matrix is ​​the target spectral curve, and the zeroth column is the other spectral curves. The calculation method of the first row and nth column elements is: D[1,n]=|D[0,n]-D[1,0]|+D[1,n-1]; the calculation method of the first row and first column elements is: D[n,1]=|D[n,0]-D[0,1]|+D[n-1,1]; the calculation method of the remaining pth row and qth column elements is: D[p,q]= |D[0,q]-D[p,0]|+min(D[p-1,q],D[p,q-1],D[p-1,q-1]); Step 1.3: After calculating the cumulative distance matrix, read the value in the last row and last column of the matrix as the result of the DTW algorithm; Step 1.4: Compare the DTW algorithm results of different polarization spectrum curves with the target curve, and use the DTW algorithm result of the curve similar to the target curve as the DTW algorithm threshold.

3. The polarization spectrum automatic frequency stabilization method based on dynamic time planning adjustment algorithm according to claim 1 is characterized in that: The specific steps of corresponding the midpoint of the scanning signal to the midpoint of the locking edge are as follows: Step 5.1: Read the time a corresponding to the midpoint position of the current locking edge and the time b corresponding to the midpoint value of the rising edge of the triangle wave; Step 5.2: Determine whether a and b are equal. If a is greater than b, increase the DC level; if a is less than b, decrease the DC level; if a=b, keep the current DC level unchanged.

4. The polarization spectrum automatic frequency stabilization method based on dynamic time planning adjustment algorithm according to claim 1 is characterized in that: The specific steps of removing the triangular wave access feedback signal to complete the locking are as follows: Step 6.1: Reduce the triangle wave amplitude by a certain amount each time, and adjust the midpoint of the scanning signal to correspond to the midpoint of the locking edge until the triangle wave signal is reduced to 0; Step 6.2: Access the feedback signal to complete frequency locking.

5. The polarization spectrum automatic frequency stabilization method based on dynamic time planning adjustment algorithm according to claim 1 is characterized in that: The field programmable logic gate array circuit generates a triangle wave and a DC level signal by a DA circuit.

6. The polarization spectrum automatic frequency stabilization method based on dynamic time planning adjustment algorithm according to claim 2 is characterized in that: During scanning in step 3, the current polarization spectrum curve is collected each time the minimum step of the scanning signal is increased, and the DTW algorithm is used to compare it with the target polarization spectrum curve in step 1.1, and the last value of the cumulative distance matrix is ​​read.

7. The polarization spectrum automatic frequency stabilization method based on dynamic time planning adjustment algorithm according to claim 2 is characterized in that: In step 4, if the final value obtained in step 3 is less than the threshold in step 1.4, it is considered that the current polarization spectrum curve is very similar to the target polarization spectrum curve, which means that the scanning signal has scanned to the required spectral line position. If the final value obtained in step 3 is greater than the threshold in step 1.4, repeat step 3 until a spectrum curve less than the threshold is obtained.

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