Laser linewidth determination method, apparatus, and computer device

Abstract

The application relates to a laser linewidth determination method, device and computer equipment. The method comprises the following steps: obtaining target interference spectrum information in the form of a modified sine curve by modifying initial interference spectrum information according to the initial interference spectrum information and a preset frequency shift frequency, and further extracting spectrum peak value information and spectrum valley value information from the target interference spectrum information based on a preset data extraction strategy to determine the laser linewidth. In the method, the target interference spectrum information obtained based on the modification strategy is in the form of a sine curve, so that the influence of the coherent envelope is eliminated during the laser linewidth measurement process, and no additional correction factor is needed, thereby improving the accuracy of the laser linewidth determination.

Description

Technical Field

[0001] This application relates to the field of linewidth measurement technology, and in particular to a laser linewidth determination method, apparatus and computer equipment. Background Technology

[0002] Narrow-linewidth single-frequency lasers have extremely important applications in fields such as optical atomic clocks, coherent communication, precision measurement, gravitational wave detection, and low-noise microwave generation. In these applications, the laser linewidth is one of the key factors determining the measurement range and accuracy. Therefore, accurate measurement of the laser linewidth is of great significance.

[0003] In existing time-delay autoheterodyne interferometry methods, when the delay fiber is much shorter than the coherence time of the laser being measured, the resulting heterodyne interferogram can also be used to measure the laser linewidth. However, the coherent envelope present in the heterodyne interferogram leads to inaccurate estimation of extrema, and the measured heterodyne interferogram may contain significant noise, resulting in low accuracy in linewidth estimation. Summary of the Invention

[0004] Therefore, it is necessary to provide a laser linewidth determination method, apparatus, and computer equipment that can effectively reduce the measurement error of laser linewidth to address the above-mentioned technical problems.

[0005] Firstly, this application provides a method for determining laser linewidth. The method includes:

[0006] Based on a preset heterodyne interferometry strategy, initial interferometric spectrum information is obtained;

[0007] The initial interference spectrum information is corrected based on the initial interference spectrum information and the preset frequency shift to determine the target interference spectrum information; the target interference spectrum in the target interference spectrum information is in sine and cosine form.

[0008] According to a preset data extraction strategy, spectral peak information and spectral valley information are extracted from the target interference spectral information;

[0009] The linewidth information of the laser under test is determined based on the peak and valley information of the spectrum.

[0010] In one embodiment, the step of correcting the initial interference spectrum information based on the initial interference spectrum information and a preset frequency shifting frequency to determine the target interference spectrum information includes:

[0011] The square of the difference between the frequency of each frequency point in the initial interference spectrum information and the preset frequency shifting frequency is used as the target correction factor;

[0012] Based on the target correction factor and the initial interferometric spectrum information, candidate interferometric spectrum information is determined;

[0013] Based on a preset screening strategy, the target interference spectrum information is selected from the candidate interference spectrum information.

[0014] In one embodiment, the step of filtering out the target interferometric spectrum information from the candidate interferometric spectrum information based on a preset filtering strategy includes:

[0015] The candidate interference spectrum information corresponding to the frequency range whose difference from the preset frequency shift frequency is greater than the target frequency threshold is used as the target interference spectrum information.

[0016] In one embodiment, the step of extracting spectral peak information and spectral valley information from the target interference spectral information according to a preset data extraction strategy includes:

[0017] Based on a preset Bayesian parameter extraction strategy, the peak spectral information and the valley spectral information are determined according to the target interference spectrum information.

[0018] In one embodiment, determining the spectral peak information and the spectral valley information based on the target interference spectral information according to the preset Bayesian parameter extraction strategy includes:

[0019] Based on a preset extended Kalman filter strategy, the peak spectral information and the valley spectral information are determined according to the target interference spectrum information.

[0020] In one embodiment, determining the spectral peak information and the spectral valley information based on the target interference spectral information according to the preset Bayesian parameter extraction strategy includes:

[0021] Based on a preset unscented Kalman filter strategy, the peak spectral information and the valley spectral information are determined according to the target interference spectrum information.

[0022] In one embodiment, the laser linewidth determination method further includes:

[0023] The initial interference spectrum information includes a delay time and a laser coherence time, wherein the delay time is much shorter than the laser coherence time.

[0024] Secondly, this application also provides a laser linewidth determination device. The device includes:

[0025] The acquisition module is used to acquire initial interference spectrum information based on a preset heterodyne interferometry strategy;

[0026] The target spectrum information determination module is used to correct the initial interference spectrum information based on the initial interference spectrum information and a preset frequency shifting frequency, and determine the target interference spectrum information; the target interference spectrum in the target interference spectrum information is in sine and cosine form;

[0027] The parameter extraction module is used to extract spectral peak information and spectral valley information from the target interference spectral information according to a preset data extraction strategy.

[0028] The linewidth information determination module is used to determine the linewidth information of the laser under test based on the spectral peak information and the spectral valley information.

[0029] In one embodiment, the target spectrum information determination module is specifically used for:

[0030] The square of the difference between the frequency of each frequency point in the initial interference spectrum information and the preset frequency shifting frequency is used as the target correction factor;

[0031] Based on the target correction factor and the initial interferometric spectrum information, candidate interferometric spectrum information is determined;

[0032] Based on a preset screening strategy, the target interference spectrum information is selected from the candidate interference spectrum information.

[0033] In one embodiment, the target spectrum information determination module is specifically used for:

[0034] The candidate interference spectrum information corresponding to the frequency range whose difference from the preset frequency shift frequency is greater than the target frequency threshold is used as the target interference spectrum information.

[0035] In one embodiment, the parameter extraction module is specifically used for:

[0036] Based on a preset Bayesian parameter extraction strategy, the peak spectral information and the valley spectral information are determined according to the target interference spectrum information.

[0037] In one embodiment, the parameter extraction module is specifically used for:

[0038] Based on a preset extended Kalman filter strategy, the peak spectral information and the valley spectral information are determined according to the target interference spectrum information.

[0039] In one embodiment, the parameter extraction module is specifically used for:

[0040] Based on a preset unscented Kalman filter strategy, the peak spectral information and the valley spectral information are determined according to the target interference spectrum information.

[0041] In one embodiment, the initial interference spectrum information includes a delay time and a laser coherence time, wherein the delay time is much shorter than the laser coherence time.

[0042] Thirdly, this application also provides a computer device. The computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to perform the steps described in the first aspect.

[0043] Fourthly, this application also provides a computer-readable storage medium. The computer-readable storage medium stores a computer program thereon, which, when executed by a processor, performs the steps described in the first aspect above.

[0044] This application provides a method, apparatus, and computer device for determining laser linewidth. In this method, the initial interference spectrum information of the laser under test is corrected based on the initial interference spectrum information and a preset frequency shift to obtain corrected sine and cosine form target interference spectrum information. Furthermore, based on a preset data extraction strategy, peak and valley information are extracted from the target interference spectrum information to determine the laser linewidth. Since the target interference spectrum information obtained based on the correction strategy is in sine and cosine form, the influence of the coherent envelope is eliminated during laser linewidth measurement, eliminating the need for additional correction factors. The terminal can directly calculate the laser linewidth using the peak and valley values ​​of the corrected heterodyne interference spectrum. The method provided in this application not only reduces the large error in laser linewidth measurement caused by measurement noise but also allows the acquisition of hundreds or thousands of linewidth estimates using a single heterodyne interference spectrum, thus providing the mean and variance of the linewidth. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a flowchart illustrating a laser linewidth determination method in one embodiment;

[0047] Figure 2 This is a schematic diagram of a short-fiber self-delay heterodyne interferometer in one embodiment;

[0048] Figure 3 This is a flowchart illustrating the laser linewidth determination method in another embodiment.

[0049] Figure 4The results show the calculated spectrum of self-delay heterodyne interference in short optical fibers under typical parameters.

[0050] Figure 5 It is the self-delay heterodyne interference spectrum of a short fiber under typical parameters multiplied by (f-f0). 2 The resulting sine-cosine spectrum;

[0051] Figure 6 The spectrum of short fiber self-delay heterodyne interferometry measured based on the structure of a short fiber self-delay heterodyne interferometer;

[0052] Figure 7 Yes Figure 6 The interference spectrum shown is multiplied by (f-f0). 2 The resulting sine-cosine spectrum;

[0053] Figure 8 In one embodiment, the sine and cosine spectrum S(f)(f-f0) is given. 2 The waveform obtained by extended Kalman filtering, as well as the amplitude and bias at each frequency point;

[0054] Figure 9 This is the linewidth calculation result obtained by extended Kalman filtering in one embodiment;

[0055] Figure 10 In another embodiment, the sine spectrum S(f)(f-f0) is... 2 The waveform obtained after unscented Kalman filtering, and the amplitude and bias at each frequency point;

[0056] Figure 11 This is the linewidth calculation result obtained from extended Kalman filtering in another embodiment;

[0057] Figure 12 This is a structural block diagram of a laser linewidth determination device in one embodiment;

[0058] Figure 13 This is an internal structural diagram of a computer device in one embodiment. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0060] In one embodiment of this application, such as Figure 1As shown, a method for determining laser linewidth is provided. This embodiment illustrates the application of this method to a terminal (which can be called a management terminal). It is understood that this method can also be applied to a server, and to a system including both a terminal and a server, and is implemented through interaction between the terminal and the server. The terminal can be, but is not limited to, various personal computers and laptops. The server can be a standalone server or a server cluster composed of multiple servers. In this embodiment, the method includes the following steps:

[0061] Step 101: Obtain initial interference spectrum information based on the preset heterodyne interferometry strategy.

[0062] The preset heterodyne interferometry strategy may include splitting the laser under test into two paths, delaying one path, and interfering with the other path (which is not delayed), thereby allowing the terminal to obtain initial interference spectrum information (self-heterodyne interference spectrum information). The laser delay can be achieved by inputting the laser under test into a delay fiber; this application can select delay fibers of different lengths to accomplish the above function. It should be noted that the method of delaying one laser path includes, but is not limited to, using a delay fiber.

[0063] Furthermore, the terminal can flexibly select delay fiber of different lengths to measure the laser linewidth, and can also flexibly select different delay methods. It can also obtain initial interference spectrum information based on different interferometer configurations. In one embodiment of this application, the terminal can obtain the initial interference spectrum information of the laser under test through a measuring device, such as... Figure 2 As shown, the laser linewidth measurement device may include a laser, a beam splitter, an optical fiber coupler, a time-delay fiber, an acousto-optic modulator (AOM) and its driver, a photodetector, and a spectrum analyzer. The laser under test is connected to the optical fiber beam splitter. The two outputs of the beam splitter are connected to the time-delay fiber and the acousto-optic modulator (AOM), respectively. The outputs of the time-delay fiber and the acousto-optic modulator (AOM) are then combined by another optical fiber coupler and connected to the photodetector to obtain a heterodyne interference signal. This signal is then input into the spectrum analyzer to obtain the heterodyne interference spectrum, i.e., the initial interference spectrum information. At this time, the power spectrum of the heterodyne interference signal (i.e., the initial interference spectrum information) can be expressed as:

[0064]

[0065] In the formula, Δν is the linewidth of the laser, f0 is the frequency shift of the acousto-optic modulator (AOM) (i.e., the preset frequency shift), and td p0 is the delay time, and p0 is the rated power of the laser under test.

[0066] Due to the delay time (t) generated when the optical signal passes through the delay fiber... d Since the frequency of the laser is much smaller than the coherence time of the laser, white noise dominates, and the influence of 1 / f noise is not significant (where f is the frequency of the laser under test). When analyzing the power spectrum S(f) of the heterodyne interference signal, only white noise is considered. Formula (1) can be expressed as:

[0067]

[0068] In the formula,

[0069] Step 102: Correct the initial interference spectrum information based on the initial interference spectrum information and the preset frequency shift to determine the target interference spectrum information; the target interference spectrum in the target interference spectrum information is in sine and cosine form.

[0070] The data processing steps for calculating the linewidth evaluation value by the terminal based on the data processing of the initial interferometric spectrum include: correcting the initial interferometric spectrum information based on the frequency information of each frequency point in the initial interferometric spectrum information and the preset frequency shifting frequency, so that the spectral form in the initial interferometric spectrum information is transformed into a sine-cosine form. Since the target interferometric spectrum is in sine-cosine form, there is no need to introduce a correction factor related to the order when estimating the linewidth, thus eliminating the error caused by the coherent envelope in determining the linewidth.

[0071] Step 103: Extract spectral peak information and spectral valley information from the target interference spectral information according to the preset data extraction strategy.

[0072] Step 104: Determine the linewidth information of the laser to be tested based on the peak and valley information of the spectrum.

[0073] Specifically, since the target interference spectrum information is in sine and cosine form, i.e. formula (2) is approximately a sine and cosine formula, the terminal can directly estimate the linewidth of the laser to be measured based on the peak and valley information in the target spectrum information.

[0074] In the aforementioned laser linewidth determination method, the terminal corrects the initial interference spectrum information based on the initial interference spectrum information and a preset frequency shift to obtain the corrected sine and cosine form of the target interference spectrum information. Furthermore, based on a preset data extraction strategy, it extracts spectral peak and valley information from the target interference spectrum information to determine the laser linewidth. In this method, since the target interference spectrum information obtained based on the correction strategy is in sine and cosine form, the influence of the coherent envelope is eliminated during laser linewidth measurement, eliminating the need for additional correction factors. The terminal can directly calculate the laser linewidth using the peak and valley values ​​of the corrected heterodyne interference spectrum. This method not only reduces the significant error in laser linewidth measurement caused by measurement noise but also allows for the acquisition of hundreds or thousands of linewidth estimates using a single heterodyne interference spectrum, thus providing the mean and variance of the linewidth.

[0075] In one embodiment of this application, such as Figure 3 As shown, step 102 above, which corrects the initial interference spectrum information based on the initial interference spectrum information and the preset frequency shifting frequency, to determine the target interference spectrum information, includes:

[0076] Step 301: Use the square of the difference between the frequency of each frequency point in the initial interference spectrum information and the preset frequency shifting frequency as the target correction factor.

[0077] Specifically, for each frequency point in the initial interference spectrum information, the terminal can determine (f-f0) based on the corresponding frequency f and the preset frequency shifting frequency f0. 2 And use it as the target correction factor for that frequency point.

[0078] Step 302: Determine candidate interferometric spectrum information based on the target correction factor and the initial interferometric spectrum information.

[0079] Specifically, for each frequency point, the terminal can set the target correction factor (f-f0) for that frequency point. 2 Multiplying this by the initial interference spectrum information S(f) yields a sine-cosine function S(f)(f-f0). 2 .

[0080] Step 303: Based on the preset screening strategy, the target interferometric spectrum information is selected from the candidate interferometric spectrum information.

[0081] In one embodiment of this application, the initial interference spectrum information includes a delay time and a laser coherence time, wherein the delay time is much shorter than the laser coherence time.

[0082] The delay time t is due to the fiber length used in the scheme protected in this application. d Much smaller than the laser coherence time 1 / Δν, thus allowing us to determine 2πt. dΔν << 1.

[0083] In one embodiment of this application, step 303 above, based on a preset screening strategy, filters out target interferometric spectrum information from candidate interferometric spectrum information, including:

[0084] The candidate interference spectrum information corresponding to the frequency range whose difference from the preset frequency shift frequency is greater than the target frequency threshold is used as the target interference spectrum information.

[0085] Since the spectra close to the preset frequency shift frequency in the candidate interferometric spectrum information show a large deviation, the terminal needs to filter out the target interferometric spectrum information in a sine-cosine form from the candidate interferometric spectrum information based on a preset screening strategy. That is, it needs to consider the region in the candidate interferometric spectrum that is far away from the carrier frequency f0 (i.e., the preset frequency shift frequency), i.e., |f-f0|>>Δν, and since δ(f-f0)(f-f0) 2 =0, based on the above formula (2), we can obtain S(f)(f-f0) 2 Approximately:

[0086]

[0087] Formula (3) above clearly shows that, based on the laser linewidth determination method described above, the terminal obtains the filtered S(f)(f-f0). 2 The target interference spectrum information is in sine and cosine form, which can effectively eliminate the influence of coherent envelope without the need for additional correction factors. This simplifies the laser linewidth determination process and improves the accuracy of laser linewidth determination.

[0088]

[0089]

[0090] Based on the above formulas (4)-(5), the terminal can determine the laser linewidth according to the peak and valley information of the target interference spectrum and the delay time of the delay fiber. Based on the target interference spectrum, the terminal can also determine the peak and valley information of each frequency point, and then obtain hundreds or thousands of linewidth estimates based on a single heterodyne interference spectrum, thereby giving the mean and variance of the linewidth.

[0091] In one embodiment of this application, step 103, which involves extracting spectral peak information and spectral valley information from the target interference spectral information according to a preset data extraction strategy, includes:

[0092] Based on a preset Bayesian parameter extraction strategy, the peak and valley information of the spectrum are determined according to the target interference spectrum information.

[0093] It should be noted that formulas (3)-(5) are theoretical calculation formulas for target interference spectrum information. The target interference spectrum information obtained by the actual terminal may contain various noise information. The peak and valley information of the spectrum extracted directly from the target interference spectrum information will have certain errors, which will lead to a large error in the measured laser linewidth information. In addition, based on the limited number of peaks and valleys in the target interference spectrum information, only a few peaks and valleys can be obtained, making it difficult to obtain statistically significant statistical quantities such as the mean and variance of the linewidth measurement.

[0094] like Figure 4 The image shows the heterodyne interference spectrum for typical parameters. For ease of comparison, Figure 4 (a) and Figure 4 (b) Corresponding to logarithmic and linear coordinates respectively. At this point, the length difference between the two interferometric fiber arms is 2 km, and the AOM frequency shift (preset shift frequency) is 80 MHz. Figure 4 The heterodyne interference spectrum shown is multiplied by (f-f0). 2 We obtain S(f)(f-f0). 2 ,like Figure 5 As shown in (a) and (b). From Figure 5 It can be seen that, except around 80MHz, S(f)(f-f0) 2 The spectral distribution information is very close to that of the sine and cosine functions, which proves the effectiveness of equation (3).

[0095] In one embodiment of this application, the laser used is a Toptica CTL1550 with a nominal linewidth of less than 10 kHz, the frequency shift of the acousto-optic modulator is 80 MHz, the delay fiber is approximately 300 meters long, and the heterodyne interference spectrum (initial interference spectrum information) S(f) directly measured on the spectrum analyzer is as follows: Figure 6 As shown. Figure 7 Given Figure 6 Multiply by (f - f0) 2 The resulting sine-cosine function S(f)(f-f0) 2 Spectrum information. Figure 6 and Figure 7 It can be seen that although S(f)(f-f0) 2 It closely approximates sine and cosine waves, but due to the significant measurement noise introduced during the measurement process, therefore... Figure 7 The curve has many burrs and noise. The noise and burrs mainly manifest in two aspects: firstly, Figure 6 The troughs of frequencies below 77MHz and above 83MHz are close to the noise floor of the spectrum analyzer; secondly, Figure 7 The noise is very high near each peak. Therefore, directly based on... Figure 7 Calculating line width based on the peaks and troughs will introduce a large error.

[0096] To address these issues, in one embodiment of this application, the terminal utilizes a Bayesian estimation method to treat the amplitude and bias of the heterodyne interferometric spectrum (i.e., the target interferometric spectrum information) as parameters of a sine and cosine function, thereby obtaining an estimated linewidth at each frequency point in the target interferometric spectrum information.

[0097]

[0098] Max[S(f)(f-f0) 2 ]=amp(f)+bias(f) (7)

[0099] Min[S(f)(f-f0) 2 ] = amp(f) - bias(f) (8)

[0100] In equation (6), amp(f) and bias(f) are the corrected quasi-sine heterodyne interference spectra S(f)(f-f0), respectively. 2 Equations (7) and (8) give the amplitude and bias at each frequency point, respectively, for S(f)(f-f0). 2 The method for calculating the maximum and minimum values. Therefore, the terminal uses the Bayesian parameter estimation method to obtain S(f)(f-f0). 2 After estimating the amplitude and bias values ​​amp(f) and bias(f) at each frequency point, we use equations (7) and (8) to obtain S(f)(f-f0) for each frequency point. 2 The maximum and minimum values ​​are obtained, and finally, combined with the above formula (5), the estimated value Δν of the laser linewidth to be measured at each frequency point can be obtained.

[0101] The terminal can use Bayesian estimation to calculate the peak and valley values ​​at each frequency point based on the corrected target interferometric spectrum information, thereby obtaining the linewidth estimate at each frequency point. This method uses only one heterodyne interferometric spectrum to obtain hundreds or thousands of laser linewidth estimates. Based on all the obtained laser linewidth estimates, statistically significant parameters such as linewidth and variance can be obtained, allowing the calculation of the mean and uncertainty, greatly reducing measurement time and improving measurement accuracy.

[0102] The laser linewidth determination method provided in this application performs mathematical transformations on the initial interference spectrum information and filters out target interference spectrum information with a sine-cosine function-like form based on a preset screening strategy. Therefore, it effectively eliminates order-related correction factors during the laser linewidth determination process, significantly improving the accuracy of the laser linewidth determination. Furthermore, based on a preset Bayesian parameter extraction strategy, the terminal can use each frequency point in the target interference spectrum information for linewidth evaluation, obtaining estimates of the amplitude and bias corresponding to each frequency point, thereby obtaining the statistically significant mean and variance of the laser linewidth to be measured. In addition, the terminal, based on Bayesian parameter estimation technology, can greatly suppress noise information in the target interference spectrum information, significantly improving the accuracy of the laser linewidth determination.

[0103] In one embodiment of this application, based on a preset Bayesian parameter extraction strategy, spectral peak information and spectral valley information are determined according to the target interference spectral information, including:

[0104] Based on a preset extended Kalman filter strategy, the peak and valley information of the spectrum are determined according to the target interference spectrum information.

[0105] In one embodiment of this application, the terminal utilizes an extended Kalman filter to perform a sine-cosine function S(f)(f-f0). 2 The amplitude and bias are estimated to minimize the impact of measurement noise on linewidth estimation and achieve accurate evaluation of the linewidth of the laser under test.

[0106] The extended Kalman filter method first requires modeling, giving the state transfer equation and the measurement equation. The quasi-sine function shown in equation (3) can be expressed as:

[0107] y(v)=A0+A c cos(T d ν+θ)+n(v) (9)

[0108] In equation (9), A0 and A c T d θ and θ are unknowns, representing the bias, amplitude, frequency, and phase of the sine wave, respectively. n(ν) is Gaussian white noise with zero mean. The four-component state variables are x(ν|ν) = [x1(ν|ν), x2(ν|ν), x3(ν|ν), x4(ν|ν)]. T x1, x2, x3, and x4 represent the cosine function A0 + A c cos(T d ν+θ), conjugate sine function A0+A c sin(T d ν+θ), “frequency” T d With the bias A0. Therefore, the state transition equation is:

[0109] x(ν|ν-1)=f(x(ν-1|ν-1)) (10)

[0110]

[0111] The measurement equation is: y(ν)=x1(ν|ν)+w(ν)=Hx(ν|ν)+w(ν)(12)

[0112] Where w(ν) represents the white noise introduced during the measurement process, including electronic noise and optical noise.

[0113] Since the state transition equation is nonlinear, the operator needs to be linearized through a local expansion of f(x) to achieve the extended Kalman filter. The Jacobian matrix of f(x) is defined as follows.

[0114]

[0115] Thus, the equations required for the extended Kalman filter procedure are listed in equations (14), (15), and (16):

[0116] x(ν|ν)=f(x(ν-1|ν-1))+K(ν)(y(ν)-Hx(ν-1|ν-1)) (14)

[0117] K(ν)=P(ν)H T (HP(ν)H T +r) -1 (15)

[0118] P(ν+1)=F(ν)[P(ν)-K(ν)HP(ν)]F T (ν)+Q (16)

[0119] Where r is the covariance matrix of the measurement noise, which is a 1*1 matrix in this invention; Q is the covariance matrix of the process noise, which is a diagonal matrix in this invention, i.e., Q = Diagonal[0,0,q1,q2]. During calculation, the values ​​of r, q1, and q2 need to be set according to the actual situation. P(0) is the identity matrix, i.e., P(0) = Diagonal[1,1,1,1].

[0120] Equations (10) to (15) constitute the extended Kalman filter implementation S(f)(f-f0). 2 The complete equations for parameter estimation. After iterative calculation, S(f)(f-f0) can be obtained based on x1, x2, and x4 at each frequency point. 2 The magnitude, and Figure 7 The peaks and troughs shown:

[0121] Amp(ν|ν)=((x1(ν|ν)-x4(ν|ν)) 2 +(x2(ν|ν)-x4(ν|ν)) 2 ) 1 / 2 (17)

[0122] maxima(ν)=x4(ν|ν)+Amp(ν|ν) (18)

[0123] minima(ν)=x4(ν|ν)-Amp(ν|ν) (19)

[0124] According to equations (18), (19) and (5), the linewidth estimate can be calculated at each frequency point. Since the resolution of heterodyne interference spectrum can be as low as kHz or even Hz, there are tens of thousands of frequency points in the spectrum, so tens of thousands of linewidth estimates can be obtained at each frequency point, and statistically significant linewidth parameters, namely mean and standard deviation, can be calculated.

[0125] It is worth noting that, because the heterodyne interference spectrum obtained in the experiment has a noise floor comparable to the minimum value of the interference spectrum in the frequency range below 77MHz and above 83MHz, such as... Figure 6 As shown; furthermore, in the central region between 79.25MHz and 80.75MHz, Figure 7 There is a significant deviation from the ideal sine and cosine functions because the approximation condition 2πt is not well satisfied. d Δν << 1. To reduce the impact of these undesirable factors and obtain a more accurate linewidth estimate, this implementation scheme selects data between 77MHz-79.25MHz and 80.75MHz-83MHz for extended Kalman filtering, respectively. Regions not used due to undesirable factors are marked with shaded areas in the figure.

[0126] Figure 8 The extended Kalman filter algorithm described above is used to apply the filter to S(f)(f-f0). 2 The results obtained from noise reduction and parameter estimation are shown in the figure. As can be seen from the figure, by using extended Kalman filtering, a more ideal cosine function, sine function and their bias can be obtained from the original measurement data with large noise, as well as the amplitude at each frequency point obtained by equation (17). Figure 9 The linewidth estimate at each frequency point is calculated according to equation (5). Based on these linewidth estimates, the average linewidth in this embodiment is 4.1kHz, and the standard deviation is 0.3kHz. Therefore, in this embodiment, the linewidth estimate obtained by using the extended Kalman filter method is: Δν=4.1kHz±0.30kHz.

[0127] In one embodiment of this application, based on a preset Bayesian parameter extraction strategy, spectral peak information and spectral valley information are determined according to the target interference spectral information, including:

[0128] Based on a preset unscented Kalman filter strategy, the peak and valley information of the spectrum are determined according to the target interference spectrum information.

[0129] In one embodiment of this application, the terminal uses unscented Kalman filtering to estimate the amplitude and bias of a sine-cosine function, thereby obtaining estimates of the linewidth, mean, and standard deviation at each frequency point.

[0130] The state transition equation and measurement equation for the unscented Kalman filter are the same as those in the extended Kalman filter algorithm, that is, the state variables are x(ν|ν)=[x1(ν|ν), x2(ν|ν), x3(ν|ν), x4(ν|ν)] T ,

[0131] The state transition equation is:

[0132] x(ν|ν-1)=f(x(ν-1|ν-1)) (20)

[0133]

[0134] The measurement equation is: y(ν)=x1(ν|ν)+w(ν)=Hx(ν|ν)+w(ν) (22)

[0135] For unscented Kalman filtering, an unscented transform is required first.

[0136] xx 0,ν-1 =x(ν-1|ν-1) (23)

[0137]

[0138]

[0139]

[0140] Where N is the number of elements in state variable x, which is N = 4 in this embodiment; parameter λ = α 2 NN, the parameter α is typically around 10 -3 Between 1 and 1; It can be obtained by performing Cholesky decomposition on P(ν-1). Representation matrix The element in the i-th column.

[0141] The weighting coefficient is defined as follows:

[0142]

[0143]

[0144]

[0145] Perform state evolution and state update on the state variables after the above unscented transformation, i.e.

[0146] xx i,ν|ν-1 =f(xx) i,ν-1 (30)

[0147]

[0148]

[0149] γ i,ν|ν-1 =h(xx) i,ν|ν-1 (33)

[0150]

[0151]

[0152]

[0153] K = P xy (P yy ) -1 (37)

[0154] P(ν)=P v|ν-1 -KP xy K T (38)

[0155] x(ν|ν)=x(ν|ν-1)+K(y(ν)-y(ν|ν-1)) (39)

[0156] The meanings of Q and r in equations (32) and (35) are consistent with those in equations (15) and (16) in Example 1, which are the covariance matrices of process noise and measurement noise, respectively. Q = Diagonal[0,0,q1,q2]. When calculating, the values ​​of r and q1 and q2 need to be set according to the actual situation. P(0) is the identity matrix, i.e., P(0) = Diagonal[1,1,1,1].

[0157] Based on the unscented Kalman filter algorithm described above, S(f)(f-f0) can be filtered. 2 Denoising and parameter estimation were performed, and the results are as follows: Figure 10 and Figure 11As shown. It can be concluded that the terminal can use unscented Kalman filtering to obtain a more ideal cosine function, sine function, their bias, and the amplitude at each frequency point obtained by equation (17). Figure 11 The linewidth estimate is obtained according to equation (5). Based on these linewidth estimates, the average linewidth is 4.1 kHz, and the standard deviation is 0.28 kHz. Therefore, in this embodiment, the linewidth estimate obtained using the unscented Kalman filter is: Δν = 4.1 kHz ± 0.28 kHz. This is in very good agreement with the results of the extended Kalman filter algorithm.

[0158] It should be understood that although the steps in the flowcharts of the above embodiments are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the above embodiments may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0159] Based on the same inventive concept, this application also provides a laser linewidth determination device for implementing the laser linewidth determination method described above. The solution provided by this device is similar to the solution described in the above method; therefore, the specific limitations in one or more embodiments of the laser linewidth determination device provided below can be found in the limitations of the laser linewidth determination method described above, and will not be repeated here.

[0160] like Figure 12 As shown, this application also provides a laser linewidth determining device 120, which includes:

[0161] The acquisition module 121 is used to acquire initial interference spectrum information based on a preset heterodyne interferometry strategy;

[0162] The target spectrum information determination module 122 is used to correct the initial interference spectrum information based on the initial interference spectrum information and the preset frequency shifting frequency, and determine the target interference spectrum information; the target interference spectrum in the target interference spectrum information is in sine and cosine form;

[0163] The parameter extraction module 123 is used to extract spectral peak information and spectral valley information from the target interference spectral information according to a preset data extraction strategy.

[0164] The linewidth information determination module 124 is used to determine the linewidth information of the laser under test based on the peak and valley information of the spectrum.

[0165] In one embodiment of this application, the target spectrum information determination module 122 is specifically used for:

[0166] The square of the difference between the frequency of each frequency point in the initial interference spectrum information and the preset frequency shift frequency is used as the target correction factor;

[0167] Based on the target correction factor and the initial interferometric spectrum information, the candidate interferometric spectrum information is determined;

[0168] Based on a preset screening strategy, the target interferometric spectrum information is selected from the candidate interferometric spectrum information.

[0169] In one embodiment of this application, the target spectrum information determination module 122 is specifically used for:

[0170] The candidate interference spectrum information corresponding to the frequency range whose difference from the preset frequency shift frequency is greater than the target frequency threshold is used as the target interference spectrum information.

[0171] In one embodiment of this application, the parameter extraction module 123 is specifically used for:

[0172] Based on a preset Bayesian parameter extraction strategy, the peak and valley information of the spectrum are determined according to the target interference spectrum information.

[0173] In one embodiment of this application, the parameter extraction module 123 is specifically used for:

[0174] Based on a preset extended Kalman filter strategy, the peak and valley information of the spectrum are determined according to the target interference spectrum information.

[0175] In one embodiment of this application, the parameter extraction module 123 is specifically used for:

[0176] Based on a preset unscented Kalman filter strategy, the peak and valley information of the spectrum are determined according to the target interference spectrum information.

[0177] In one embodiment of this application, the initial interference spectrum information includes a delay time and a laser coherence time, wherein the delay time is much shorter than the laser coherence time.

[0178] In one embodiment of this application, a computer device is provided, which may be a terminal, and its internal structure diagram may be as follows. Figure 13As shown, the computer device includes a processor, memory, communication interface, display screen, and input devices connected via a system bus. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs stored in the non-volatile storage media. The communication interface is used for wired or wireless communication with external terminals; wireless communication can be achieved through Wi-Fi, mobile cellular networks, NFC (Near Field Communication), or other technologies. When executed by the processor, the computer program implements a laser linewidth determination method. The display screen can be an LCD screen or an e-ink display screen. The input devices can be a touch layer covering the display screen, buttons, a trackball, or a touchpad mounted on the computer device casing, or an external keyboard, touchpad, or mouse.

[0179] Those skilled in the art will understand that Figure 13 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0180] In one embodiment of this application, a computer device is provided, including a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the steps in the above-described method.

[0181] In one embodiment of this application, a computer-readable storage medium is provided, on which a computer program is stored, which, when executed by a processor, implements the steps in the above-described method.

[0182] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties.

[0183] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium. When executed, the computer program can include the processes of the embodiments of the above methods. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0184] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0185] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for determining laser linewidth, characterized in that, The method includes: Based on a preset heterodyne interferometry strategy, initial interferometric spectrum information is obtained; the initial interferometric spectrum information includes delay time and laser coherence time, wherein the delay time is much shorter than the laser coherence time; The frequencies of each frequency point in the initial interference spectrum information and preset frequency shift The square of the difference is used as the target correction factor; The target correction factor and the initial interference spectrum information Multiplying the results yields a quasi-sine / cosine function; this quasi-sine / cosine function represents candidate interference spectrum information. Based on a preset screening strategy, target interference spectrum information is selected from the candidate interference spectrum information; the target interference spectrum information is in a sine-cosine form. Based on a preset Bayesian parameter extraction strategy, the peak and valley information of the spectrum are determined according to the target interference spectrum information. Based on the peak and valley information of the spectrum, the linewidth information of the laser to be tested is determined. The method based on the preset Bayesian parameter extraction strategy, which determines the peak and valley information of the spectrum according to the target interference spectrum information, and determines the linewidth information of the laser to be measured according to the peak and valley information, includes: Based on the preset Bayesian parameter extraction strategy, the estimated values ​​of the amplitude and bias of the quasi-sine function at each frequency point are obtained. The maximum and minimum values ​​of the quasi-sine function at each frequency point are determined by the sum and difference of the estimated values ​​of the amplitude and bias at each frequency point. Then, the estimated value of the linewidth of the laser to be measured at each frequency point is determined by formula (1). ; Formula (1) is: ,in, The maximum value of the quasi-sine function corresponding to each frequency point; The minimum value of the quasi-sine function corresponding to each frequency point; The delay time is mentioned.

2. The laser linewidth determination method according to claim 1, characterized in that, The step of filtering out target interferometric spectrum information from the candidate interferometric spectrum information based on a preset filtering strategy includes: The candidate interference spectrum information corresponding to the frequency range whose difference from the preset frequency shift frequency is greater than the target frequency threshold is used as the target interference spectrum information.

3. The laser linewidth determination method according to claim 1, characterized in that, The method based on the preset Bayesian parameter extraction strategy, which determines the spectral peak information and spectral valley information according to the target interference spectral information, includes: Based on a preset extended Kalman filter strategy, the peak and valley information of the spectrum are determined according to the target interference spectrum information.

4. The laser linewidth determination method according to claim 1, characterized in that, The method based on the preset Bayesian parameter extraction strategy, which determines the spectral peak information and spectral valley information according to the target interference spectral information, includes: Based on a preset unscented Kalman filter strategy, the peak and valley information of the spectrum are determined according to the target interference spectrum information.

5. A laser linewidth determination device, characterized in that, The device includes: The acquisition module is used to acquire initial interference spectrum information based on a preset heterodyne interferometry strategy; the initial interference spectrum information includes delay time and laser coherence time, wherein the delay time is much shorter than the laser coherence time; The target spectrum information determination module is used to determine the frequencies of each frequency point in the initial interference spectrum information. Difference between the preset frequency shift and the preset frequency shift The square of the value is used as the target correction factor; the target correction factor and the initial interference spectrum information are then combined. Multiplying the results yields a quasi-sine function; this quasi-sine function represents candidate interference spectrum information; based on a preset filtering strategy, target interference spectrum information is selected from the candidate interference spectrum information; the target interference spectrum information is in quasi-sine form. The parameter extraction module is used to determine the peak and valley information of the spectrum based on the target interference spectrum information according to a preset Bayesian parameter extraction strategy. The linewidth information determination module is used to determine the linewidth information of the laser to be tested based on the peak spectral information and the valley spectral information. The parameter extraction module and the linewidth information determination module are specifically used to obtain the estimated values ​​of the amplitude and bias of the quasi-sine function at each frequency point based on a preset Bayesian parameter extraction strategy, and to determine the maximum and minimum values ​​of the quasi-sine function corresponding to each frequency point by using the sum and difference of the estimated values ​​of the amplitude and bias at each frequency point, respectively, and then to determine the estimated value of the linewidth of the laser to be measured corresponding to each frequency point by using formula (1). ; Formula (1) is: ,in, The maximum value of the quasi-sine function corresponding to each frequency point; The minimum value of the quasi-sine function corresponding to each frequency point; The delay time is mentioned.

6. The apparatus according to claim 5, characterized in that, The target spectrum information determination module is specifically used to take the candidate interference spectrum information corresponding to the frequency range whose difference from the preset frequency shift frequency is greater than the target frequency threshold as the target interference spectrum information.

7. The apparatus according to claim 5, characterized in that, The parameter extraction module is specifically used to determine the peak and valley information of the spectrum based on the target interference spectrum information, according to a preset extended Kalman filter strategy.

8. The apparatus according to claim 5, characterized in that, The parameter extraction module is specifically used to determine the peak and valley information of the spectrum based on the target interference spectrum information, according to a preset unscented Kalman filtering strategy.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 4.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 4.

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