Time domain correction heterodyne signal positioning method and device based on windowed fourier transform

Abstract

The application discloses a kind of based on windowed Fourier transform's time domain modified heterodyne signal positioning method and device, it is related to signal processing technical field, including: obtaining local oscillator light signal and echo signal light signal, according to local oscillator light signal and echo signal light signal, obtain local oscillator light phase and echo signal light phase;According to local oscillator light phase and echo signal light phase, using balanced detector, after filtering direct current component, obtain optical heterodyne intermediate frequency current signal;Using windowed Fourier transform identifies the maximum of optical heterodyne intermediate frequency current signal spectrum peak value, determines the initial position of optical heterodyne intermediate frequency current signal;According to the characteristics of balanced detector, obtain phase difference, and phase difference is converted into time domain difference;Using time domain difference corrects the initial position of optical heterodyne intermediate frequency current signal, obtains the accurate initial position of optical heterodyne intermediate frequency current signal.The application can obtain more accurate range intensity image.

Description

Technical Field

[0001] This invention belongs to the field of signal processing technology, specifically relating to a method and apparatus for locating time-domain corrected heterodyne signals based on windowed Fourier transform. Background Technology

[0002] Optical heterodyne detection technology, with its advantages of high conversion gain, good spectral filtering performance and strong spatial and polarization resolution, is widely used in fields such as lidar, optical communication, optical sensing and ultra-precision measurement.

[0003] Among related technologies, heterodyne detection has broad application prospects in the detection of weak targets at long distances, and it has unparalleled advantages compared with direct detection. However, because the correlation photoelectric balanced detectors currently used in detection are area integral devices, the wavefront mismatch between the signal light and the local oscillator light caused by the laser speckle field—that is, the phase mismatch problem—will cause the intermediate frequency signals generated at different locations on the balanced detector surface to cancel each other out, resulting in a severe decoherence effect. In active detection applications, such as synthetic aperture lidar, long-range coherent radar, and laser vibration measurement, the decoherence effect caused by the target surface roughness is a major obstacle limiting the practical application of optical heterodyne detection.

[0004] Existing noise suppression methods can be broadly categorized into hardware filtering and software algorithms. Hardware filtering methods typically employ high-power or narrow-band filters in lidar system design. Software algorithms include Empirical Mode Decomposition (EMD), Kalman filtering, wavelet transform, and Fourier filtering window methods. EMD filters are usually chosen when a good signal-to-noise ratio is achieved, especially during nighttime detection. However, Kalman filtering can cause short-range offsets (deviations) when the atmospheric extinction coefficient changes drastically. Particle filters have also been proposed to replace ensemble Kalman filters in denoising algorithms. While these methods can improve the signal-to-noise ratio of lidar echo signals, the location of the heterodyne signal is still affected by noise, leading to inaccurate positioning.

[0005] Therefore, it is urgent to improve the defects existing in the current technology. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention provides a method and apparatus for locating time-domain corrected heterodyne signals based on windowed Fourier transform. The technical problem to be solved by this invention is achieved through the following technical solution:

[0007] In a first aspect, the present invention provides a time-domain corrected heterodyne signal localization method based on windowed Fourier transform, comprising:

[0008] Acquire the local oscillator optical signal and the echo optical signal, and based on the local oscillator optical signal and the echo optical signal, obtain the local oscillator optical phase and the echo optical phase;

[0009] Based on the phase of the local oscillator light and the phase of the echo signal light, the optical heterodyne intermediate frequency current signal is obtained after filtering out the DC component using a balanced detector.

[0010] The maximum value of the peak value of the optical heterodyne intermediate frequency current signal is identified by using windowed Fourier transform, and the initial measurement position of the optical heterodyne intermediate frequency current signal is determined.

[0011] Based on the characteristics of the balanced detector, the phase difference is obtained and converted into a time domain difference;

[0012] The initial measurement position of the optical heterodyne intermediate frequency current signal is corrected by using time-domain difference correction, so as to obtain the actual precise position of the optical heterodyne intermediate frequency current signal.

[0013] Secondly, the present invention also provides a time-domain corrected heterodyne signal positioning device based on windowed Fourier transform, comprising:

[0014] The signal acquisition module is used to acquire the local oscillator optical signal and the echo optical signal, and to acquire the local oscillator optical phase and the echo optical phase based on the local oscillator optical signal and the echo optical signal.

[0015] The signal conversion module is used to obtain the optical heterodyne intermediate frequency current signal by filtering out the DC component using a balanced detector based on the phase of the local oscillator light and the phase of the echo signal light.

[0016] Signal processing module one is used to identify the maximum value of the peak value of the optical heterodyne intermediate frequency current signal spectrum using windowed Fourier transform, and to determine the initial measurement position of the optical heterodyne intermediate frequency current signal.

[0017] Signal processing module two is used to obtain the phase difference based on the characteristics of the balanced detector and convert the phase difference into a time domain difference;

[0018] The result output module is used to correct the initial measurement position of the optical heterodyne intermediate frequency current signal using time-domain difference correction, so as to obtain the actual precise position of the optical heterodyne intermediate frequency current signal.

[0019] The beneficial effects of this invention are:

[0020] This invention provides a time-domain corrected heterodyne signal positioning method and apparatus based on windowed Fourier transform. First, when extracting the heterodyne signal position from the time-domain signal using windowed Fourier transform for coherent lidar, noise can cause deviations, leading to inaccurate heterodyne signal positioning. Based on the principle of a balanced photodetector, this invention doubles the amplitude of the output AC signal after differential processing, eliminates the DC signal, and establishes a π phase difference between the optical heterodyne intermediate frequency current signals. This ensures that the intermediate frequency signal power obtained by the device is the sum of the intermediate frequency powers of the two devices, significantly reducing system noise. Second, the phase difference is extracted from the signal output by the balanced detector. Using the radian-angle conversion relationship, the radian phase difference is converted to an angle phase difference. The difference between the initial measurement and the actual position of the heterodyne signal in the time domain is obtained using the phase difference-time domain difference relationship. Finally, by using the obtained correction expression, the heterodyne signal position can be corrected based on the position difference and sampling interval. This invention can make necessary adjustments to the measured value of the heterodyne signal, thereby improving the accuracy of the obtained actual position.

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0022] Figure 1 This is a flowchart of a time-domain corrected heterodyne signal localization method based on windowed Fourier transform provided in an embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of a signal propagation scenario provided in an embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of a windowed Fourier transform provided in an embodiment of the present invention;

[0025] Figure 4 This is a schematic diagram of an optical heterodyne intermediate frequency current signal with Gaussian white noise provided in an embodiment of the present invention;

[0026] Figure 5 This is a schematic diagram of the spectral peak values ​​of the pure optical heterodyne intermediate frequency current signal after windowed Fourier transform and the heterodyne signal with a noisy background provided in the embodiments of the present invention;

[0027] Figure 6 (a) is a schematic diagram of a signal-to-noise ratio of -18dB provided in an embodiment of the present invention;

[0028] Figure 6 (b) is a schematic diagram of a signal-to-noise ratio of -17dB provided in an embodiment of the present invention;

[0029] Figure 6(c) is a schematic diagram of a signal-to-noise ratio of -16dB provided in an embodiment of the present invention;

[0030] Figure 6 (d) is a schematic diagram of a signal-to-noise ratio of -15dB provided in an embodiment of the present invention;

[0031] Figure 6 (e) is a schematic diagram of a signal-to-noise ratio of -14dB provided in an embodiment of the present invention;

[0032] Figure 6 (f) is a schematic diagram of a signal-to-noise ratio of -13dB provided in an embodiment of the present invention;

[0033] Figure 6 (g) is a schematic diagram of a signal-to-noise ratio of -12dB provided in an embodiment of the present invention;

[0034] Figure 6 (h) is a schematic diagram of a signal-to-noise ratio of -11dB provided in an embodiment of the present invention;

[0035] Figure 6 (i) is a schematic diagram of a signal-to-noise ratio of -10dB provided in an embodiment of the present invention;

[0036] Figure 7 This is a schematic diagram illustrating the relationship between the localization and signal-to-noise ratio of the optical heterodyne intermediate frequency current signal before and after phase compensation, provided in an embodiment of the present invention.

[0037] Figure 8 (a) is a schematic diagram of the position deviation curve of the intermediate frequency current signal of the windowed Fourier transform positioning optical heterodyne provided in an embodiment of the present invention;

[0038] Figure 8 (b) is a schematic diagram of the position deviation curve of the intermediate frequency current signal of the positioning optical heterodyne after position correction provided in an embodiment of the present invention. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0040] In related technologies, compared with direct detection methods, coherent lidar can provide higher sensitivity, eliminate the influence of background light, and obtain echo signal intensity, distance, or Doppler images through scanning. Coherent lidar can also analyze the accuracy of intensity images based on the speckle characteristics of the target. Currently, most research focuses on the theoretical study of factors affecting the ranging accuracy of coherent lidar and time-domain signal denoising methods. However, for distant non-cooperative targets, the target distance and noise both affect the extraction of target intensity images. This noise is generally considered to be caused by local oscillator (LO) shot noise, LO power supply, and detector instability. When the target echo signal itself is weak, the instability of the LO signal can exceed the amplitude of the echo signal, causing the weak echo signal generated by the target to be submerged, making it difficult to extract the target intensity image. At present, signal segmented cumulative averaging and spectral averaging methods are applied to reduce the influence of noise on weak signals, thereby improving the signal-to-noise ratio of the heterodyne signal (intermediate frequency signal). Although existing algorithms can eliminate some noise, they still cannot completely eliminate the influence of noise, resulting in unstable localization of the heterodyne signal, thus failing to obtain accurate images.

[0041] In view of this, the present invention provides a time-domain corrected heterodyne signal localization method based on windowed Fourier transform. In the case of weak echo signals being submerged, the phase correction and separation of the echo signal optical signal are performed to extract the relative intensity image of the target. The method provided by the present invention can reduce the decoherence effect without the need for additional optical equipment or hardware, and can accurately determine the precise location of the heterodyne signal. The present invention is verified by combining simulation results.

[0042] Please see Figure 1 As shown, Figure 1 This is a flowchart of a time-domain corrected heterodyne signal localization method based on windowed Fourier transform provided by an embodiment of the present invention. The time-domain corrected heterodyne signal localization method based on windowed Fourier transform provided by the present invention includes:

[0043] S101. Obtain the local oscillator optical signal and the echo optical signal, and obtain the local oscillator optical phase and the echo optical phase based on the local oscillator optical signal and the echo optical signal.

[0044] Specifically, please see Figure 2 As shown, Figure 2 This is a schematic diagram of a signal propagation scenario provided in an embodiment of the present invention. In this embodiment, a signal propagation scenario is first constructed; the signal propagation scenario includes a laser, an acousto-optic modulator, a coupler, a ring splitter, a galvanometer scanning system, and a balanced detector;

[0045] The laser emits continuous light, which is split into a local oscillator beam and a signal beam via an optical fiber. The local oscillator beam is transmitted to a coupler, while the signal beam, after being modulated and frequency-shifted by an acousto-optic modulator, is transmitted to a ring splitter. The ring splitter sends the signal beam to a galvanometer scanning system, which controls the horizontal and vertical movement of the signal beam. Simultaneously, the galvanometer scanning system connects to a host computer via a USB interface and determines the scanning range of the target by receiving instructions from the host computer. The signal beam is incident on the target surface, reflected by the target, and the echo beam is incident on the ring splitter. The ring splitter inputs the signal beam to the coupler, where it couples with the local oscillator beam to form a mixed signal, which is then transmitted to a balanced detector.

[0046] Local oscillator optical signal acquired by the balanced detector The expression is:

[0047] ;

[0048] Echo signal optical signal acquired by the balanced detector The expression is:

[0049] ;

[0050] in, The complex amplitude of the local oscillator light. The unit vector representing the polarization direction of the local oscillator light. The angular frequency of the local oscillator light. For the phase of the local oscillator light, The complex amplitude of the echo signal light. The unit vector representing the polarization direction of the echo signal light. The angular frequency of the echo signal light. For the phase of the echo signal light, It is a spatial position vector. For time, It is an imaginary number. For An exponential function with base 0.

[0051] It should be noted that, in this embodiment, after optical fiber processing, two uniform plane waves with the same polarization state are obtained, namely the local oscillator beam. and signal light The acousto-optic modulator is model AOMO 3100-80 (Gooch & Housego Co., Ltd.), used for 80MHz frequency shift modulation. The galvanometer scanning system controls the horizontal and vertical movement of the signal light and determines the scanning range of the target. A ring splitter inputs the echo signal to a coupler to couple it with the local oscillator light, forming a mixed signal, which is then transmitted to a balanced detector. Finally, the echo signal and the local oscillator light signals are acquired and processed by an AD acquisition card and a computer.

[0052] S102. Based on the phase of the local oscillator light and the phase of the echo signal light, after filtering out the DC component using a balanced detector, the optical heterodyne intermediate frequency current signal is obtained.

[0053] Specifically, in this embodiment, after the local oscillator optical signal and the echo optical signal are processed by a balanced detector, the DC component is filtered out, and the output signal containing only the difference frequency term, i.e., the optical heterodyne intermediate frequency current signal, is output. Its expression is:

[0054] (1);

[0055] ;

[0056] in, For electron charge, To balance the quantum efficiency of the detector, The average photon energy, ω is the angular frequency of the optical heterodyne intermediate frequency current signal.

[0057] It should be noted that in formula (1) It is the time average over the optical frequency period.

[0058] In this embodiment, the propagation direction and polarization state of the signal light and the local oscillator light are set to be the same, simplifying the optical heterodyne intermediate frequency current signal and simplifying subsequent calculations; the simplified expression of the optical heterodyne intermediate frequency current signal is:

[0059]

[0060] ;

[0061] in, To balance the detector's responsivity.

[0062] It should be noted that by setting the propagation direction and polarization state of the signal light and the local oscillator light to be the same, the unit vector of the polarization direction of the echo signal light... The unit vector of the polarization direction of the local oscillator light Complex amplitude of local oscillator light The complex amplitude of the echo signal light The impact can be disregarded.

[0063] S103. Use windowed Fourier transform to identify the maximum value of the peak value of the optical heterodyne intermediate frequency current signal spectrum, and determine the initial measurement position of the optical heterodyne intermediate frequency current signal.

[0064] Specifically, please see Figure 3 As shown, Figure 3 This is a schematic diagram of a windowed Fourier transform provided in an embodiment of the present invention. In this embodiment, the initial measurement position of the optical heterodyne intermediate frequency current signal is obtained through the following process:

[0065] S1031. Divide the optical heterodyne intermediate frequency current signal into segments according to a fixed window step size; where the window step size is the sampling interval.

[0066] S1032. Following the windowing method, perform Fourier transform on the optical heterodyne intermediate frequency current signal within each sampling interval sequentially to obtain the spectral peak value within each sampling interval. Its expression is:

[0067] ;

[0068] ;

[0069] ;

[0070] in, is the real part of the Fourier transform. This is the optical heterodyne intermediate frequency current signal. For natural index, The imaginary unit, The angular frequency of the signal. For time, This represents the imaginary part of the Fourier transform.

[0071] S1033. Compare the magnitude of the spectral peaks within each sampling interval, determine the largest spectral peak, and obtain the corresponding window. The position of this window is the initial measurement position of the optical heterodyne intermediate frequency current signal.

[0072] It should be noted that in this embodiment, when identifying the peak value of the optical heterodyne intermediate frequency current signal spectrum, the window width is set to 10s, and the window step size is determined by the sampling interval. In this embodiment, 0.1s is selected.

[0073] S104. Based on the characteristics of the balanced detector, obtain the phase difference and convert the phase difference into a time domain difference.

[0074] Specifically, in this embodiment, firstly, the phase of the optical heterodyne intermediate frequency current signal is obtained based on the imaginary and real parts of the Fourier transform. Its expression is:

[0075] ;

[0076] in, for The unit of angle, that is, the conversion relationship between radians and degrees, can be used to convert radians into degrees. Convert to angle system Its expression is:

[0077] ;

[0078] in, Pi is the mathematical constant of a circle.

[0079] In this embodiment, considering that the initial measurement position of the optical heterodyne intermediate frequency current signal extracted from the time-domain signal by the coherent lidar using windowed Fourier transform may have a certain degree of deviation due to noise, making it impossible to accurately determine the optical heterodyne intermediate frequency current signal; the balanced detector actually has two built-in channels, using two laser diodes with completely similar characteristics as photoelectric conversion, with a delay line added to one channel, or a Mach-Zehnder interferometer used at the front end to adjust the phase reverse bias of one channel, so that there is a gap between the optical heterodyne intermediate frequency current signals. The phase difference is determined; a differential amplifier is used at the back end to amplify the differential-mode signal and suppress the common-mode signal. After adding the two signals, the power of the optical heterodyne intermediate frequency current signal obtained by the balanced detector is the sum of the power of the optical heterodyne intermediate frequency current signals detected by the two laser diodes. After differential processing, the noise cancels each other out, greatly reducing the system noise and significantly amplifying the output amplitude. That is, based on the characteristics of the balanced detector itself, the phase difference can be determined. for:

[0080] (2);

[0081] In this embodiment, the method further includes converting the phase difference into a time domain difference. The transformation relationship is as follows:

[0082] (3);

[0083] in, For phase difference, The frequency of the optical heterodyne intermediate frequency current signal is denoted as .

[0084] Substituting formula (2) into formula (3), we get:

[0085] ;

[0086] It should be noted that the phase difference can be used to calculate the deviation between the actual position and the simulated position in the time domain. This allows for compensation, resulting in the precise location of the optical heterodyne intermediate frequency current signal.

[0087] S105. Use time-domain difference correction to correct the initial measurement position of the optical heterodyne intermediate frequency current signal to obtain the actual precise position of the optical heterodyne intermediate frequency current signal.

[0088] Specifically, in this embodiment, a correction function is first constructed, the expression of which is:

[0089] ;

[0090] The initial measurement position of the optical heterodyne intermediate frequency current signal Sampling interval time and time domain difference The actual position of the corrected optical heterodyne intermediate frequency current signal is obtained from the input correction function. It can achieve position correction of optical heterodyne signals, thereby improving the accuracy of data acquisition. The use of weak signal coherent lidar improves the accuracy of target position and can obtain more accurate distance intensity images.

[0091] In an optional embodiment of the present invention, the effectiveness of the method provided by the present invention is verified by simulation experiments.

[0092] I. Simulation Parameters

[0093] Please see Figure 2As shown, a coherent lidar experimental system was constructed. First, a continuous-wave laser with a center wavelength of 532 nm, a linewidth of 5 MHz, and a maximum power of 2 W was used to output the laser. The laser was split into a local oscillator beam and a signal beam. The signal beam was frequency-shifted and modulated by an acousto-optic modulator (AOM) with a shift amplitude of 80 MHz. The modulator was triggered by an external TTL (transistor-to-transistor logic level) signal with a frequency of 10 kHz and a pulse width of 200 ns. The modulated signal beam was then modulated into a 5 μJ pulse energy signal beam by an electro-optic modulator and then sent to the galvanometer scanning system via a ring splitter. In the scanner, the beam became a parallel beam after passing through a focusing lens and was precisely positioned and controlled in two directions by a combination of two orthogonal galvanometers. One galvanometer controlled the horizontal movement of the beam, while the other controlled the vertical movement. Simultaneously, the system connects to a host computer via a USB interface, receiving commands from the host computer to scan at a specific angle, thus determining the scanning range. After modulation by the detected target, the echo beam is input to the coupler through a ring splitter to couple with the local oscillator beam, forming a mixed signal, namely the optical heterodyne intermediate frequency current signal. The coupler ensures energy transmission and matching between the echo signal and the local oscillator beam in the system, ensuring the quality and stability of the mixed signal. The interference information between the two beams is detected by a balanced detector. Due to the limited bandwidth of the photodetector, care should be taken to ensure that the intermediate frequency signal after the two beams beat during detection is within the detector's response bandwidth. The balanced detector outputs a photocurrent signal, which is then processed by an amplifier to obtain the intermediate frequency heterodyne signal. An AD acquisition card is used to acquire and record signal information at a frequency of 500MHz. The signal data acquired by the acquisition card is transmitted to the computer for processing via a network cable.

[0094] In this simulation experiment, a signal-to-noise ratio of 10dB, an intermediate frequency of 0.6Hz, and a phase difference of [missing information] are simulated. The optical heterodyne intermediate frequency current signal was used, with the number of pre-acquired signals set to 42, a signal width of 10 seconds, and a sampling interval of 0.1 seconds. Please refer to [link / reference]. Figure 4 As shown, Figure 4 This is a schematic diagram of an optical heterodyne intermediate frequency current signal with Gaussian white noise provided in an embodiment of the present invention. Figure 4 As can be seen, the original optical heterodyne intermediate frequency current signal is completely submerged in noise, making it impossible to directly distinguish the location of the optical heterodyne intermediate frequency current signal. The frequency of the optical heterodyne intermediate frequency current signal is 30MHz, and the resolution of the Fourier transform can be expressed as... ,in, Sampling frequency, For sampling points, the lowest frequency resolution used in optical heterodyne intermediate frequency current signal processing is 5MHz.

[0095] II. Simulation Content

[0096] By simulating traditional positioning methods and performing conventional denoising on the noise signal, and obtaining the spectral peak value by performing a windowed Fourier transform on the optical heterodyne intermediate frequency current signal, the positioning search process can be simulated and the initial measurement position of the optical heterodyne intermediate frequency current signal can be determined. Please refer to [link to relevant documentation]. Figure 5 As shown, Figure 5 This is a schematic diagram illustrating the spectral peak values ​​of the pure optical heterodyne intermediate frequency current signal after windowed Fourier transform and the heterodyne signal with a noisy background, provided in an embodiment of the present invention. Figure 5 As can be seen from the blue curve, the spectral peaks of the pure light heterodyne intermediate frequency current signal exhibit a regular and smooth stepped shape. This regularity is maintained near the peaks, and there are no irregular fluctuations. From the magnified detail front view, the maximum value is 42, meaning the localization value of the heterodyne signal under noise-free conditions is 42, which matches the initial setting. Figure 5 In the green curve, we can see that the spectral peaks of the heterodyne signal under noise do not exhibit a regular stepped shape, and the frequency band fluctuations near the maximum value also lack a fixed pattern. Compared with the spectral peak curve of the clean heterodyne signal, the trends of the two are generally consistent, but the green curve has more jitter and spikes caused by noise. The front view more intuitively shows the difference, and the location of the maximum spectral peak of the green curve is also shown. The value is 48, while the actual position of the signal is 42. This means that peak extraction is inaccurate under noisy conditions, and there is a significant positioning deviation, making traditional methods no longer applicable.

[0097] When the correction method proposed in this invention is used for correction, the initial measurement position will be observed without phase compensation. =48. The phase is determined through steps S101-S104. It is -0.8796. After converting to degrees, The value is -50.40°. Subsequently, the relationship between phase difference and time difference is used to quantify the deviation between the actual and simulated positions in the time domain. This results in the deviation generated by the time-domain signal. It was determined to be 0.6. Meanwhile, the sampling interval... The value is selected as 0.1s, and finally, the corrected position is obtained through step S105. The value is 42, consistent with the true position. Therefore, the proposed phase compensation method can correct the position of the heterodyne signal.

[0098] To test the stability of the proposed correction method, since noise is random, the initial positioning may change randomly, potentially leading to inaccurate positioning of the optical heterodyne intermediate frequency current signal. To verify the stability of this algorithm, simulation analysis was performed to examine the impact of signal-to-noise ratio variations on positioning. Please refer to [link to relevant documentation]. Figure 6As shown in (a) to 6(i), the localization values ​​before and after the compensation algorithm were compared for different signal-to-noise ratios. Figure 6 (a) is a schematic diagram of a signal-to-noise ratio of -18dB provided in an embodiment of the present invention. Figure 6 (b) is a schematic diagram of a signal-to-noise ratio of -17dB provided in an embodiment of the present invention. Figure 6 (c) is a schematic diagram of a signal-to-noise ratio of -16dB provided in an embodiment of the present invention. Figure 6 (d) is a schematic diagram of a signal-to-noise ratio of -15dB provided in an embodiment of the present invention. Figure 6 (e) is a schematic diagram of a signal-to-noise ratio of -14dB provided in an embodiment of the present invention. Figure 6 (f) is a schematic diagram of a signal-to-noise ratio of -13dB provided in an embodiment of the present invention. Figure 6 (g) is a schematic diagram of a signal-to-noise ratio of -12dB provided in an embodiment of the present invention. Figure 6 (h) is a schematic diagram of a signal-to-noise ratio of -11dB provided in an embodiment of the present invention. Figure 6 (i) is a schematic diagram of a signal-to-noise ratio of -10dB provided in an embodiment of the present invention, as shown below. Figure 6 As shown in (a) and 6(b), under conditions of extremely poor signal-to-noise ratio, both the signal before and after compensation deviate from the accurate positioning value of 42; Figure 6 In (c) and 6(d), when the signal-to-noise ratio is slightly improved, the positioning accuracy after algorithm compensation can be significantly improved; however, the positioning before phase compensation still has a large deviation. Figure 6 (e) Initially, the algorithm-compensated positioning values ​​are stably distributed around the accurate value 42; as the signal-to-noise ratio increases, the positioning deviation before compensation also decreases, but there is still a significant deviation from the accurate value 42; such as Figure 6 As shown in (i), even at the optimal signal-to-noise ratio, the positioning before phase compensation is stable at around 47, still deviating from the accurate value by 5.

[0099] Please see Figure 7 As shown, Figure 7 This is a schematic diagram illustrating the relationship between the positioning and signal-to-noise ratio (SNR) of the optical heterodyne intermediate frequency current signal before and after phase compensation, provided in an embodiment of the present invention. The horizontal axis represents the SNR range from -18dB to -10dB, and the vertical axis represents the absolute deviation from the precise value of 42. To ensure accuracy, seven experiments were conducted for each SNR value to obtain the positioning values ​​before and after phase compensation, and the average absolute deviation value was calculated. Figure 7The graph uses red spheres and blue stars to represent two curves, showing the trends in the absolute values ​​of the positioning error before and after phase compensation. The results show that the positioning error decreases both before and after compensation as the signal-to-noise ratio (SNR) increases. However, even under the worst SNR conditions, the average positioning error after compensation (deviation value of 16) is lower than before compensation (deviation value of 20). It should be noted that as the SNR slowly increases (the horizontal axis changes from -17dB to -15dB), the absolute value of the average positioning error after compensation decreases rapidly (from the initial deviation value of 15 to the deviation value of 4), and the curve drops sharply. During the same period, the positioning error before compensation only decreases from the initial deviation value of 18 to the deviation value of 10. With further increases in SNR, the absolute value of the position error after phase compensation almost decreases to zero; in other words, accurate positioning can be achieved with heterodyne signals. It should be noted that at this time, the absolute value of the positioning deviation before phase compensation still falls within the range of 4-6. The results show that even under low signal-to-noise ratio conditions, the phase correction method proposed in this invention can effectively achieve accurate positioning. As the signal-to-noise ratio increases slightly, the positioning accuracy using this method is greatly improved, and the positioning error is reduced to zero, far exceeding the positioning accuracy before algorithm compensation.

[0100] The simulation experiment was repeated 1000 times to further analyze the effect of the algorithm compensation, such as... Figure 8 As shown in (a) to 8(b), Figure 8 (a) is a schematic diagram of the position deviation curve of the intermediate frequency current signal of the windowed Fourier transform positioning optical heterodyne provided in an embodiment of the present invention. Figure 8 (b) is a schematic diagram of the position deviation curve of the intermediate frequency current signal of the positioning optical heterodyne after phase correction provided in an embodiment of the present invention. Figure 8 (a) shows the direct positioning results without phase compensation, with an average deviation of 6.56 after 1000 experiments. Here, deviation refers to the deviation from the precise value of 42. Figure 8 (b) shows the positioning results after phase compensation, with an average deviation of 3.45; from Figure 8 As can be seen from (a) to (b), the point deviation after compensation is significantly reduced, which further verifies the effectiveness of the phase compensation method proposed in this invention.

[0101] Based on the same inventive concept, this invention also provides a time-domain corrected heterodyne signal localization device based on windowed Fourier transform, applied to the time-domain corrected heterodyne signal localization method based on windowed Fourier transform provided in the above embodiments of this invention, including:

[0102] The signal acquisition module is used to acquire the local oscillator optical signal and the echo optical signal, and to acquire the local oscillator optical phase and the echo optical phase based on the local oscillator optical signal and the echo optical signal.

[0103] The signal conversion module is used to obtain the optical heterodyne intermediate frequency current signal by filtering out the DC component using a balanced detector based on the local oscillator light phase and the echo signal light phase;

[0104] Signal processing module one is used to identify the maximum value of the peak value of the optical heterodyne intermediate frequency current signal spectrum using windowed Fourier transform, and to determine the initial measurement position of the optical heterodyne intermediate frequency current signal.

[0105] Signal processing module two is used to obtain the phase difference based on the characteristics of the balanced detector and convert the phase difference into a time domain difference;

[0106] The result output module is used to correct the initial measurement position of the optical heterodyne intermediate frequency current signal using the time domain difference, so as to obtain the actual precise position of the optical heterodyne intermediate frequency current signal.

[0107] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that an article or device comprising a list of elements includes not only those elements but also other elements not expressly listed. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device comprising said element. Terms such as "connected" or "linked" are not limited to physical or mechanical connections but can include electrical connections, whether direct or indirect. The orientations or positional relationships indicated by terms such as "upper," "lower," "left," and "right" are based on the orientations or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention.

[0108] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0109] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A time-domain corrected heterodyne signal localization method based on windowed Fourier transform, characterized in that, include: Acquire the local oscillator optical signal and the echo optical signal, and obtain the local oscillator optical phase and the echo optical phase based on the local oscillator optical signal and the echo optical signal; Based on the local oscillator phase and the echo signal phase, the optical heterodyne intermediate frequency current signal is obtained after filtering out the DC component using a balanced detector. The maximum value of the peak value of the optical heterodyne intermediate frequency current signal spectrum is identified by using windowed Fourier transform, and the initial measurement position of the optical heterodyne intermediate frequency current signal is determined. The step of using windowed Fourier transform to identify the maximum value of the peak value of the optical heterodyne intermediate frequency current signal spectrum and determining the initial measurement position of the optical heterodyne intermediate frequency current signal includes: The optical heterodyne intermediate frequency current signal is divided according to a fixed window step size; wherein, the window step size is the sampling interval. Following a windowing approach, the optical heterodyne intermediate frequency current signal within each sampling interval is sequentially subjected to Fourier transform to obtain the spectral peak value within each sampling interval. Its expression is: ； ； ； in, is the real part of the Fourier transform. This is the optical heterodyne intermediate frequency current signal. For natural index, The imaginary unit, Angular frequency, For time, This represents the imaginary part of the Fourier transform. The magnitudes of spectral peaks within each sampling interval are compared to determine the largest spectral peak, and the corresponding window is obtained. The position of this window is the initial position of the optical heterodyne intermediate frequency current signal. ; Based on the characteristics of the balanced detector, the phase difference is obtained and converted into a time domain difference; The initial measurement position of the optical heterodyne intermediate frequency current signal is corrected by the time domain difference to obtain the actual precise position of the optical heterodyne intermediate frequency current signal; It also includes: constructing a correction function, the expression of which is: ； in, To determine the precise initial position of the corrected optical heterodyne intermediate frequency current signal, This represents the initial position of the optical heterodyne intermediate frequency current signal. The sampling interval time. For time domain difference, Representing radians Convert to angle system.

2. The time-domain corrected heterodyne signal localization method based on windowed Fourier transform according to claim 1, characterized in that, Also includes: Construct a signal propagation scenario; the signal propagation scenario includes a laser, an acousto-optic modulator, a coupler, a ring splitter, a galvanometer scanning system, and a balanced detector; The laser emits continuous light, which is split into a local oscillator beam and a signal beam via an optical fiber. The local oscillator beam is transmitted to the coupler, and the signal beam, after being modulated and frequency-shifted by the acousto-optic modulator, is transmitted to the ring splitter. The ring splitter sends the signal beam to the galvanometer scanning system, which controls the horizontal and vertical movement of the signal beam. Simultaneously, the galvanometer scanning system is connected to a host computer via a USB interface and determines the scanning range of the target by receiving instructions from the host computer. The signal beam is incident on the target surface, reflected by the target, and the echo beam is incident on the ring splitter. The ring splitter inputs the signal beam to the coupler, where it couples with the local oscillator beam to form a mixed signal, which is then transmitted to the balanced detector. The local oscillator light signal acquired by the balanced detector The expression is: ； The echo signal acquired by the balanced detector The expression is: ； in, The complex amplitude of the local oscillator light. The unit vector representing the polarization direction of the local oscillator light. The angular frequency of the local oscillator light. For the phase of the local oscillator light, The complex amplitude of the echo signal light. The unit vector representing the polarization direction of the echo signal light. The angular frequency of the echo signal light. For the phase of the echo signal light, It is a spatial position vector. For time, It is an imaginary number. For An exponential function with base 0.

3. The time-domain corrected heterodyne signal localization method based on windowed Fourier transform according to claim 2, characterized in that, The optical heterodyne intermediate frequency current signal The expression is: ； ； in, For electron charge, To balance the quantum efficiency of the detector, The average photon energy, ω is the angular frequency of the optical heterodyne intermediate frequency current signal.

4. The time-domain corrected heterodyne signal localization method based on windowed Fourier transform according to claim 3, characterized in that, Also includes: The propagation direction and polarization state of the signal light and the local oscillator light are set to be the same, which simplifies the optical heterodyne intermediate frequency current signal; The simplified expression for the optical heterodyne intermediate frequency current signal is: ； in, To balance the detector's responsivity.

5. The time-domain corrected heterodyne signal localization method based on windowed Fourier transform according to claim 1, characterized in that, The phase difference The expression is: ； ； ； in, The phase of the optical heterodyne intermediate frequency current signal.

6. The time-domain corrected heterodyne signal localization method based on windowed Fourier transform according to claim 1, characterized in that, The time domain difference The expression is: ； in, For phase difference, The frequency of the optical heterodyne intermediate frequency current signal is denoted as .

7. A time-domain corrected heterodyne signal localization device based on windowed Fourier transform, used to implement the method as described in any one of claims 1-6, characterized in that, include: The signal acquisition module is used to acquire the local oscillator optical signal and the echo optical signal, and to acquire the local oscillator optical phase and the echo optical phase based on the local oscillator optical signal and the echo optical signal. The signal conversion module is used to obtain the optical heterodyne intermediate frequency current signal by filtering out the DC component using a balanced detector based on the local oscillator light phase and the echo signal light phase; Signal processing module one is used to identify the maximum value of the peak value of the optical heterodyne intermediate frequency current signal spectrum using windowed Fourier transform, and to determine the initial measurement position of the optical heterodyne intermediate frequency current signal. Signal processing module two is used to obtain the phase difference based on the characteristics of the balanced detector and convert the phase difference into a time domain difference; The result output module is used to correct the initial measurement position of the optical heterodyne intermediate frequency current signal using the time domain difference, so as to obtain the accurate actual position of the optical heterodyne intermediate frequency current signal.

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