An ultra-wideband fast electromagnetic environment perception device and its perception method

Abstract

The present invention relates to an ultra-wideband fast electromagnetic environment perception device and its perception method, which includes two parts: a front-end electric field sensor module and a back-end optoelectronic processing module. Based on two femtosecond pulse lasers with repetition frequencies of 213.226 MHz and 216.495 MHz and a dual-channel co-polarized optical electric field sensor, undersampling of broadband signals is performed, and finally fast perception of wideband signals is achieved, reducing its received bandwidth to within the range of 110 MHz. The back-end optoelectronic processing module can be collected using a 250 MHz data acquisition card, reducing the sampling rate requirement of the back-end acquisition device and improving the single-shot measurement speed of the system's full frequency band. The device is provided with functions of real-time measurement of the repetition frequency and real-time adjustment of the link optical power, ensuring the accuracy and stability of the system measurement, and greatly improving the environmental adaptability.

Description

Technical Field

[0001] The present invention belongs to the field of electric field sensing, and in particular to an ultra-wideband fast electromagnetic environment sensing device based on a femtosecond pulse light source and a sensing method thereof. Background Art

[0002] Electromagnetic environment sensing plays an important role in electromagnetic compatibility (EMC) design. The development of electronic technology has led to an increase in the complexity of devices in the electronic power system. Many devices are integrated into the same system or platform, with complex spectral components and increased mutual interference between devices, making the electromagnetic compatibility problem more prominent. Therefore, electromagnetic compatibility has become an important indicator for measuring the performance of a device or system. During the electromagnetic compatibility design process, engineering designers need to pre-iterate "design - test - re-design" according to the internal electromagnetic emission characteristics of the device, locate the interference source step by step, check for possible electromagnetic compatibility problems, and continuously improve the device performance.

[0003] Electromagnetic environment sensing is of great significance in military affairs. The development of electronic technology has promoted the development of military equipment. The complexity of the spectral information of the frequency-using equipment of the equipment has led to the complexity of the battlefield electromagnetic environment. Under the requirement of joint operations in the land, sea, air, space, and electromagnetic domains, the mastery of battlefield electromagnetic environment information directly determines the outcome of victory. Electromagnetic environment sensing can be applied to electromagnetic environment situation awareness, comprehensively master the distribution of the battlefield electromagnetic environment from multiple dimensions of time - space - frequency - energy, master the electromagnetic environment information of the enemy and us, and ensure our advantageous position.

[0004] Traditional electromagnetic environment sensing mostly uses an antenna plus a superheterodyne receiver. Although a superheterodyne receiver can achieve a very high frequency band, there is a contradiction between the sweep speed and the measurement sensitivity. For rapidly changing signals (such as ultra-short pulses), it is easy to miss sampling during the frequency sweep process, thus unable to obtain complete electromagnetic environment information. The channelized receiver receives through multiple channels, which can improve the receiving speed, but the equipment is complex and the cost is high. For the battlefield where a large number of sensors need to be deployed, the cost is huge. With the development of microwave photon technology, electromagnetic signal receiving devices based on microwave photonics have developed rapidly. Among them, the instantaneous frequency measurement technology can obtain an extremely wide instantaneous bandwidth and is suitable for applications in occasions with high requirements for frequency bands and response speeds such as radar warning. However, its measurement error rate is relatively high when dealing with complex multi-frequency electromagnetic environments, and the frequency measurement accuracy is relatively low, making it difficult to achieve more accurate electromagnetic environment sensing. Summary of the Invention

[0005] Technical Problems to be Solved

[0006] Aiming at the defects existing in the prior art, in order to achieve accurate and rapid electromagnetic environment perception, the present invention proposes an ultra-wideband rapid electromagnetic environment perception device and its perception method, which includes two parts: a front-end electric field sensor module and a back-end optoelectronic processing module. Based on two femtosecond pulse lasers with repetition frequencies of 213.226 MHz and 216.495 MHz and a dual-channel co-polarized optical electric field sensor, the present invention undersamples broadband signals and finally realizes rapid perception of wideband signals, reducing its receiving bandwidth to within the range of 110 MHz. The back-end optoelectronic processing module can be collected using a 250 MHz data acquisition card, reducing the sampling rate requirement of the back-end acquisition device and improving the single-shot measurement speed of the entire frequency band of the system (less than 1 s). The device is provided with functions of real-time measurement of the repetition frequency and real-time adjustment of the link optical power to ensure the accuracy and stability of system measurement, and greatly improve the environmental adaptability.

[0007] The technical solutions adopted are as follows:

[0008] An ultra-wideband rapid electromagnetic environment perception device includes two parts: a front-end electric field sensor module and a back-end optoelectronic processing module. Among them, the front-end electric field sensor module includes a dual-channel co-polarized electric field sensor and two polarization-maintaining long optical fibers; the back-end optoelectronic processing module includes the following parts: a femtosecond pulse laser with a repetition frequency of 213.226 MHz, a femtosecond pulse laser with a repetition frequency of 216.495 MHz, two 1:9 polarization-maintaining optical splitters, two polarization-maintaining circulators, two 1 GHz electro-optic modulators, four photodetectors, four 110 MHz low-pass filters, a 4-channel 250 MHz sampling rate ADC, two 1:9 single-mode optical splitters, a dual-channel optical power monitoring module, a computer, several polarization-maintaining optical fibers, several single-mode optical fibers, and several RF cables; among them, the two femtosecond pulse lasers are respectively connected to the two 1:9 polarization-maintaining optical splitters through polarization-maintaining optical fibers. 90% of the output laser passes through the polarization-maintaining optical fiber and is input into the polarization-maintaining circulator, and 10% of the output laser passes through the single-mode optical fiber and is input into the electro-optic modulator; the laser output from the polarization-maintaining circulator is connected to the dual-channel co-polarized electric field sensor through the polarization-maintaining optical fiber, and the other path is connected to the 1:9 single-mode optical splitter; 90% of the output lasers of the two electro-optic modulators and the two 1:9 single-mode optical splitters are connected to the input ends of the four photodetectors. The output signals of the four photodetectors are connected to the low-pass filter through RF cables and then enter the ADC. The computer calculates the electromagnetic environment information based on the ADC sampling signals; the input end of the dual-channel optical power monitoring module is connected to 10% of the output lasers of the two 1:9 single-mode optical splitters, and the output end of the dual-channel optical power monitoring module is connected to the computer. The computer controls the output power of the two femtosecond pulse lasers based on the monitoring information of the dual-channel optical power monitoring module.

[0009] Further, the operating frequency band of the ultra-wideband fast electromagnetic environment perception device covers 1 MHz - 40 GHz, and the single measurement speed of the full frequency band is less than 1 s.

[0010] Further, the requirement for the two-way consistency of the two-way co-polarized electric field sensor is that the difference in the response function is less than 3 dB.

[0011] Further, it also includes two 53 MHz signal source modules, which are connected to the electro-optic modulator through the 53 MHz signal source modules to calibrate the real-time repetition frequency of the transmitted laser.

[0012] Further, an optical power adjustment module is provided inside the two femtosecond pulse lasers.

[0013] Further, it also includes several RS232 serial communication data lines. Based on the magnitude of the reflected optical power obtained in the optical power monitoring module, the computer controls the optical power adjustment modules of the two femtosecond pulse lasers through the RS232 serial communication data lines to adjust the output optical power. The perception method based on the ultra-wideband fast electromagnetic environment perception device includes the following steps:

[0014] S1: The two femtosecond pulse lasers simultaneously emit pulsed light. After passing through a 1:9 polarization-maintaining optical splitter, 90% of the laser enters the polarization-maintaining circulator, and 10% of the laser enters a 1 GHz electro-optic modulator.

[0015] S2: The 90% of the laser passes through the polarization-maintaining circulator and enters the front-end co-polarized electric field sensor. The surrounding electromagnetic environment is collected through the electric field sensor and is reflected back to the circulator. After being separated from the upstream light by the circulator, it enters channels 3 and 4 of the four-channel photodetector.

[0016] S3: The electrical signals output by the four-channel photodetector enter a 200 MHz low-pass filter and then are input into channels 3 and 4 of the shown ADC for sampling.

[0017] S4: The 10% of the laser enters the 1 GHz electro-optic modulator, and the electro-optic modulator is connected to the 53 MHz signal source module; the light output by the electro-optic modulator is connected to channels 1 and 2 of the photodetector, and the electrical signals output by the photodetector enter channels 1 and 2 of the ADC after passing through a 200 MHz low-pass filter.

[0018] S5: The computer obtains the reflected optical power from the optical power monitoring module through the RS232 serial communication data line and adjusts the output optical power of the two lasers through the RS232 serial communication data line to ensure that the optical power entering channels 3 and 4 of the photodetector is -4 dBm, so as to ensure the stability of the system output.

[0019] S6: Input the data of channels 1 - 4 of the ADC into a computer for spectrum calculation to obtain electromagnetic environment information.

[0020] Furthermore, the calculation method for obtaining electromagnetic environment information based on the multi-channel ADC in step S6 is as follows:

[0021] First, use channels 1 and 2 of the ADC to obtain the accurate repetition frequencies of two light sources, specifically as follows:

[0022] (1) Perform FFT on the data output from channels 1 and 2 of the ADC.

[0023] (2) Obtain the first frequency peak point f11 near 53MHz and the second frequency peak point f12 near 53MHz in channel 1. Then, the accurate real-time repetition frequency of the 213.226MHz repetition frequency femtosecond pulse laser is F1 = f11 + f12.

[0024] (3) Obtain the first frequency peak point f21 near 53MHz and the second frequency peak point f22 near 53MHz in channel 2. Then, the accurate real-time repetition frequency of the 216.495MHz repetition frequency femtosecond pulse laser is F2 = f21 + f22.

[0025] Then, process the output signals of channels 3 and 4 of the ADC to obtain the initial spectrum in the electromagnetic environment to be measured.

[0026] Finally, based on the repetition frequencies F1, F2 and the initial spectrum, recover the optical undersampling frequency through the remainder matching method, and then solve the frequency information of the electromagnetic signal to be measured.

[0027] The beneficial effects of the present invention compared with the prior art:

[0028] 1. The present invention uses a femtosecond pulse light source to undersample high-frequency signals, compresses electromagnetic signals from 1MHz to 40GHz within the range of 110MHz for reception, reduces the requirement for the sampling rate of the backend ADC, and a sampling rate of only 250MHz can meet the reception of signals within 40GHz.

[0029] 2. The present invention uses a 200MHz low-pass filter to filter the electro-optic conversion signal, filters out the electrical pulse signal converted by the light source pulse, and eliminates its influence on the system dynamic range.

[0030] 3. In order to avoid the influence of repetition frequency drift on the measurement accuracy of the system, the present invention uses a 53MHz signal generation module and a 1GHz electro-optic modulator to monitor the repetition frequency.

[0031] 4. The present invention realizes the stability of the system output by monitoring the optical power and regulating the output of the light source. Brief Description of the Drawings

[0032] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0033] Figure 1 It is a schematic diagram of the composition of the ultra-wideband fast electromagnetic environment perception device of the present invention;

[0034] Figure 2 It is a software interface diagram of the ultra-wideband fast electromagnetic environment perception device of the present invention;

[0035] Figure 3 It is a flowchart for calculating electromagnetic environment information based on multiple ADCs of the present invention.

[0036] Description of the reference numerals:

[0037] 1 - 213.226 MHz repetition rate femtosecond pulse laser, 2 - 216.495 MHz repetition rate femtosecond pulse laser, 3 - 1:9 polarization maintaining optical splitter, 4 - polarization maintaining circulator, 5 - 1 GHz electro-optic modulator, 6 - 1:9 single-mode optical splitter, 7 - dual-channel optical power monitoring module, 8 - four-channel photodetector, 9 - 200 MHz four-channel low-pass filter, 10 - 4-channel 250 MHz sampling rate ADC, 11 - computer, 12 - backend optoelectronic processing module, 13 - dual-channel co-polarized electric field sensor, 14 - front-end electric field sensor module, 15 - 53 MHz signal source module. Specific Embodiments

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0039] Figure 1 As shown, it is a composition diagram of the ultra-wideband fast electromagnetic environment perception device, which mainly consists of two parts: a backend optoelectronic processing module and a front-end electric field sensor.

[0040] An ultra-wideband fast electromagnetic environment perception device includes two parts: a front-end electric field sensor module 14 and a backend optoelectronic processing module 12;

[0041] Among them, the front-end electric field sensor module 14 consists of a dual-channel co-polarized electric field sensor 13 and two polarization-maintaining long optical fibers; the dual-channel consistency requirement of the dual-channel co-polarized electric field sensor 13 is that the difference in response functions is less than 3 dB. This setting ensures the synchronization of the two-channel induction data and is of great significance for the measurement of instantaneous signals.

[0042] The back-end optoelectronic processing module 12 includes the following parts: a 213.226 MHz repetition rate femtosecond pulse laser 1, a 216.495 MHz repetition rate femtosecond pulse laser 2, two 1:9 polarization-maintaining optical splitters 3, two polarization-maintaining circulators 4, two 1 GHz electro-optic modulators 5, four-channel photodetectors 8, four-channel 110 MHz low-pass filters 9, a 4-channel 250 MHz sampling rate ADC 10 (analog-to-digital converter), two 1:9 single-mode optical splitters 6, a dual-channel optical power monitoring module 7, a computer 11, several polarization-maintaining optical fibers, several single-mode optical fibers, and several RF cables; among them, the two femtosecond pulse lasers 1 and 2 are respectively connected to the two 1:9 polarization-maintaining optical splitters 3 through polarization-maintaining optical fibers, 90% of the output laser passes through the polarization-maintaining optical fiber and is input into the polarization-maintaining circulator 4, and 10% of the output laser passes through the single-mode optical fiber and is input into the electro-optic modulator 5; the laser output from the polarization-maintaining circulator 4 is connected to the dual-channel co-polarized electric field sensor 13 through a polarization-maintaining optical fiber, and the other path is connected to the 1:9 single-mode optical splitter 6; the output ends of the two electro-optic modulators 5 and 90% of the output laser of the two 1:9 single-mode optical splitters 6 are connected to the input ends of the four-channel photodetectors 8, the output signals of the four-channel photodetectors 8 are connected to the low-pass filter 9 through RF cables and then enter the ADC 10, the computer 11 calculates the electromagnetic environment information based on the sampling signals of the ADC 10, the input end of the dual-channel optical power monitoring module 7 is connected to 10% of the output laser of the two 1:9 single-mode optical splitters 6, the output end of the dual-channel optical power monitoring module 7 is connected to the computer 11, and the computer 11 controls the output power of the two femtosecond pulse lasers 1 and 2 based on the monitoring information of the dual-channel optical power monitoring module 7.

[0043] The operating frequency band of the ultra-wideband fast electromagnetic environment perception device covers 1 MHz - 40 GHz, and the single measurement speed in the full frequency band is less than 1 s.

[0044] The perception device further includes two 53 MHz signal source modules 15, which are connected to the electro-optic modulator through the 53 MHz signal source module to calibrate the real-time repetition frequency of the transmitted laser.

[0045] Optical power adjustment modules are provided inside the two femtosecond pulse lasers.

[0046] The sensing device further includes a number of RS232 serial communication data lines. The dual-channel optical power monitoring module 7 is connected to the computer 11 through the RS232 serial communication data lines. Based on the magnitude of the reflected optical power obtained in the optical power monitoring module 7, the computer 11 controls the optical power adjustment modules of the two femtosecond pulse lasers 1 and 2 to adjust the output optical power through the RS232 serial communication data lines.

[0047] The sensing method based on the ultra-wideband fast electromagnetic environment sensing device includes the following steps:

[0048] S1: The two femtosecond pulse lasers simultaneously emit pulsed light. After passing through a 1:9 polarization-maintaining optical splitter, 90% of the laser light enters the polarization-maintaining circulator, and 10% of the laser light enters the 1 GHz electro-optic modulator.

[0049] S2: The 90% laser light passes through the polarization-maintaining circulator and enters the front-end co-polarized electric field sensor. The surrounding electromagnetic environment is collected by the electric field sensor and reflected back to the circulator. After being separated from the upstream light by the circulator, it enters channels 3 and 4 of the four-channel photodetector.

[0050] S3: The electrical signals output by the four-channel photodetector enter the 200 MHz low-pass filter and then are input into channels 3 and 4 of the ADC for sampling.

[0051] S4: The 10% laser light enters the 1 GHz electro-optic modulator, and the electro-optic modulator is connected to the 53 MHz signal source module. The light output by the electro-optic modulator is connected to channels 1 and 2 of the photodetector. The electrical signals output by the photodetector enter channels 1 and 2 of the ADC after passing through the 200 MHz low-pass filter.

[0052] S5: The computer obtains the reflected optical power from the optical power monitoring module through the RS232 serial communication data line and adjusts the output optical power of the two lasers through the RS232 serial communication data line to ensure that the optical power entering channels 3 and 4 of the photodetector is -4 dBm, thereby ensuring the stability of the system output.

[0053] S6: The data of channels 1-4 of the ADC are input into the computer for spectrum calculation to obtain electromagnetic environment information.

[0054] Figure 2 Shown is the software interface of the ultra-wideband fast electromagnetic environment sensing device. In order to visualize the sensing results and calculated electromagnetic environment information of the ultra-wideband fast electromagnetic environment sensing device, a corresponding software interface is configured to display the above information.

[0055] Figure 3The following is a flowchart of the present invention for calculating electromagnetic environment information based on multiple ADCs. The electromagnetic environment information can be calculated from the 4-channel signals obtained by the ADC. The process is as follows:

[0056] First, use channels 1 and 2 of the ADC to obtain the precise repetition frequencies of two light sources, specifically as follows:

[0057] (1) Perform FFT on the data output from channels 1 and 2 of the ADC. FFT refers to the Fast Fourier Transform;

[0058] (2) Obtain the first frequency peak point f11 near 53MHz and the second frequency peak point f12 near 53MHz in channel 1. Then, the precise real-time repetition frequency of the 213.226MHz repetition frequency femtosecond pulse laser is F1 = f11 + f12;

[0059] (3) Obtain the first frequency peak point f21 near 53MHz and the second frequency peak point f22 near 53MHz in channel 2. Then, the precise real-time repetition frequency of the 216.495MHz repetition frequency femtosecond pulse laser is F2 = f21 + f22;

[0060] Then, process the output signals of channels 3 and 4 of the ADC. Based on the prior art, the initial spectrum in the electromagnetic environment to be measured can be obtained;

[0061] Finally, based on the repetition frequencies F1 and F2 and the initial spectrum, the optical undersampling frequency is restored by the remainder matching method, and then the frequency information of the electromagnetic signal to be measured is resolved. Among them, the optical undersampling frequency restoration by the remainder matching method is the prior art, and specific reference can be made to Chinese Patent CN 113138313B.

[0062] Obviously, the above embodiments are only examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. An ultra-wideband fast electromagnetic environment perception device, characterized in that, it includes a front-end electric field sensor module and a rear-end optoelectronic processing module. Among them, the front-end electric field sensor module includes a dual-channel co-polarized electric field sensor and two polarization-maintaining long optical fibers; the rear-end optoelectronic processing module includes the following parts: a femtosecond pulse laser with a repetition frequency of 213.226 MHz, a femtosecond pulse laser with a repetition frequency of 216.495 MHz, 2 1:9 polarization-maintaining optical splitters, 2 polarization-maintaining circulators, 2 1 GHz electro-optic modulators, four photodetectors, four 110 MHz low-pass filters, a 4-channel ADC with a sampling rate of 250 MHz, 2 1:9 single-mode optical splitters, a dual-channel optical power monitoring module, a computer, several polarization-maintaining optical fibers, several single-mode optical fibers, and several RF cables; among them, the two femtosecond pulse lasers are respectively connected to the two 1:9 polarization-maintaining optical splitters through polarization-maintaining optical fibers. 90% of the output laser is input to the polarization-maintaining circulator through the polarization-maintaining optical fiber, and 10% of the output laser is input to the electro-optic modulator through the single-mode optical fiber; the laser output from the polarization-maintaining circulator is connected to the dual-channel co-polarized electric field sensor through a polarization-maintaining optical fiber, and the other path is connected to the 1:9 single-mode optical splitter; the output ends of the two electro-optic modulators and 90% of the output laser of the two 1:9 single-mode optical splitters are connected to the input ends of the four photodetectors. The output signals of the four photodetectors are connected to the low-pass filter through RF cables and then enter the ADC. The computer calculates the electromagnetic environment information based on the ADC sampling signals; the input end of the dual-channel optical power monitoring module is connected to 10% of the output laser of the two 1:9 single-mode optical splitters, and the output end of the dual-channel optical power monitoring module is connected to the computer. The computer controls the output power of the two femtosecond pulse lasers based on the monitoring information of the dual-channel optical power monitoring module.

2. An ultra-wideband fast electromagnetic environment perception device according to claim 1, characterized in that, the operating frequency band of the ultra-wideband fast electromagnetic environment perception device covers 1 MHz - 40 GHz, and the single measurement speed of the frequency band is less than 1 s.

3. An ultra-wideband fast electromagnetic environment perception device according to claim 2, characterized in that, the dual-channel consistency requirement of the dual-channel co-polarized electric field sensor is that the response function difference is less than 3 dB.

4. An ultra-wideband fast electromagnetic environment perception device according to claim 3, characterized in that, it further includes 2 53 MHz signal source modules, which are connected to the electro-optic modulator through the 53 MHz signal source modules to calibrate the real-time repetition frequency of the transmitted laser.

5. An ultra-wideband fast electromagnetic environment perception device according to claim 4, characterized in that, optical power adjustment modules are provided inside the two femtosecond pulse lasers.

6. An ultra-wideband fast electromagnetic environment perception device according to claim 5, characterized in that, It also includes several RS232 serial communication data lines. Based on the return light power obtained in the optical power monitoring module, the computer controls the optical power adjustment modules of the two femtosecond pulse lasers through the RS232 serial communication data lines to adjust the output optical power.

7. A sensing method based on the ultra-wideband rapid electromagnetic environment sensing device as claimed in claim 6, It is characterized in that The steps include: S1: The two femtosecond pulse lasers emit pulse light simultaneously, which passes through a 1:9 polarization-maintaining beam splitter, 90% of the laser light enters a polarization-maintaining circulator, and 10% of the laser light enters a 1 GHz electro-optic modulator; S2: 90% of the laser light enters the dual-channel co-polarization electric field sensor through the polarization-maintaining circulator. After the electric field sensor collects the surrounding electromagnetic environment, the laser light is reflected back to the circulator, separated from the uplink light by the circulator, and enters the 3rd and 4th channels of the four-channel photoelectric detector; S3: The electrical signals output by the four photodetectors enter a 200 MHz low-pass filter and are then input into channels 3 and 4 of the ADC for sampling; S4: the 10% laser light enters the 1 GHz electro-optic modulator, and the 53 MHz signal source is connected to the electro-optic modulator of the module; The light output by the electro-optic modulator is connected to channels 1 and 2 of the photodetector, and the electrical signal output by the photodetector is connected to channels 1 and 2 of the ADC after passing through a 200MHz low-pass filter; S5: The computer obtains the return light power from the optical power monitoring module through the RS232 serial communication data line, and adjusts the output optical power of the two lasers through the RS232 serial communication data line to ensure that the optical power entering the photodetector channels 3 and 4 is -4dBm, thereby ensuring that the system output remains stable; S6: Inputting the 1-4 channel data of the ADC into a computer to perform spectrum calculation to obtain electromagnetic environment information.

8. The sensing method according to claim 7, It is characterized in that The calculation method for obtaining electromagnetic environment information based on the multi-channel ADC in step S6 is: First, use channels 1 and 2 of the ADC to obtain the precise repetition rate of the two light sources, as follows: (1) performing FFT on the data output by channels 1 and 2 of the ADC; (2) A first frequency peak point f11 near 53 MHz and a second frequency peak point f12 near 53 MHz are obtained in the channel 1, and the precise real-time repetition frequency of the 213.226 MHz repetition frequency femtosecond pulse laser is F1=f11+f12; (3) A first frequency peak point f21 near 53 MHz and a second frequency peak point f22 near 53 MHz are obtained in the two channels, and the precise real-time repetition frequency of the 216.495 MHz repetition frequency femtosecond pulse laser is F2=f21+f22; Then, the 3rd and 4th channel output signals of the ADC are processed to obtain the initial spectrum in the electromagnetic environment to be measured; Finally, based on the real-time repetition frequencies F1, F2 and the initial spectrum, the optical under-sampling frequency is restored by a residue matching method, thereby solving the frequency information of the electromagnetic signal to be measured.

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