A compressed ultrafast imaging system and method based on a low-pass filter

Abstract

The present invention belongs to the field of high-speed imaging technology, and discloses a low-pass filter-based compressed ultrafast imaging system and method. The present invention uses a low-pass filter as a compression component for signal acquisition, filters out the high-frequency part of the sampled signal through the low-pass filter, reduces the bandwidth of the sampled signal, and realizes signal downsampling. The present invention can effectively reduce system complexity and cost, and improve the signal-to-noise ratio of the restored image.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-speed imaging, and more specifically, relates to a compressed ultrafast imaging system and method based on a low-pass filter. Background Art

[0002] At present, compressed sensing algorithms have become a research hotspot in the field of high-speed imaging. Classical imaging technology follows the Nyquist-Shannon sampling theorem, that is, the sampling rate must be more than twice the highest frequency of the original signal, which is generally much higher than the requirements of the Nyquist sampling theorem, in order to restore the original signal. Therefore, conventional sampling will definitely collect a large amount of redundant data, which will put great pressure on data storage and processing equipment. The high-speed imaging process must meet the requirements of fast acquisition speed and signal fidelity. When the traditional Nyquist sampling rate is met, the imaging process will generate a large amount of data in a short period of time, and the back-end hardware storage and processing equipment will find it difficult to achieve continuous acquisition and real-time imaging.

[0003] In 2007, Terence Tao and others proposed the theory of compressed sensing, which is based on the sparsity of signals in the observation domain and achieves the reconstruction of data signals with a data volume far lower than that required by the Nyquist sampling theorem. Later, in 2008, Rice University in the United States first proposed combining the principle of compressed sensing with a single-pixel imaging system to develop a single-pixel compressed digital camera. By using a digital micromirror array (DMD) to achieve random subsampling of image signals, compress the original signal, and restore the image using an algorithm. This imaging method can effectively reduce the amount of data, relieve hardware pressure, and improve imaging speed. It is the basis of many current compressed sensing single-pixel imaging systems.

[0004] The encoding rate and imaging frame rate of the DMD-based compression imaging system are limited by the DMD's graphic refresh rate, and can only reach the order of hundreds of kHz at present. In 2015, Bryan T. Bosworth et al. from Johns Hopkins University proposed using a pattern generator to encode the time-domain stretched waveform of ultrafast laser pulses, and compress the encoded pulses through dispersive optical fibers, collect them through high-speed photodetectors (PDs) and analog-to-digital converters (ADCs), and restore the images by computers. The imaging frame rate of this method is determined by the repetition frequency of the laser, reaching the order of hundreds of MHz, which can achieve continuous ultrafast imaging of microscopic high-speed moving objects. However, the method of using dispersive optical fibers to achieve pulse compression usually requires more than ten kilometers of dispersive optical fibers, which will seriously lose signal power, reduce the signal-to-noise ratio, and increase the cost and complexity of the system. Summary of the invention

[0005] The present invention provides a low-pass filter-based compressed ultrafast imaging system and method to solve the problems of high signal-to-noise ratio, high system complexity and high cost in the prior art compressed ultrafast imaging.

[0006] The present invention provides a low-pass filter-based compressed ultrafast imaging system, comprising: a time domain stretching unit, a programmable structured light unit, a high-speed signal acquisition unit and a signal processing unit; the high-speed signal acquisition unit comprises a low-pass filter, and the low-pass filter is used as a compression component for signal acquisition to filter out the high-frequency part of the sampling signal, reduce the bandwidth of the sampling signal, and realize signal downsampling.

[0007] Preferably, the high-speed signal acquisition unit further comprises: a first 4f lens system, a first objective lens, a second objective lens, a second 4f lens system, a second diffraction grating, a second collimator, a high-speed photodetector and a high-speed oscilloscope;

[0008] The first 4f lens system and the first objective lens are used to focus the coded structure light signal on the surface of the sample to be tested; the light signal carrying the information of the sample to be tested passes through the second objective lens and the second 4f lens system in sequence and is incident on the second diffraction grating, and the second diffraction grating is used to compress the light signal in the spatial domain; the compressed light signal is collimated by the second collimator and input into the high-speed photodetector, and the high-speed photodetector is used to capture the sampling signal and convert the light signal into an analog electrical signal; the radio frequency signal output end of the high-speed photodetector is connected to the input end of the low-pass filter, and the output end of the low-pass filter is connected to the signal input end of the high-speed oscilloscope; the low-pass filter is used to filter out high-frequency signals in the sampling signal, and the high-speed oscilloscope reduces the channel bandwidth of the acquisition signal to be consistent with the cut-off frequency of the low-pass filter, and the high-speed oscilloscope is used to perform low sampling rate acquisition, convert the analog electrical signal into a digital signal, and transmit it to the signal processing unit.

[0009] Preferably, the high-speed signal acquisition unit uses a plurality of series-connected low-pass filters as compression components for signal acquisition.

[0010] Preferably, the time domain stretching unit comprises: a mode-locked femtosecond laser and a dispersive optical fiber; the optical signal output end of the mode-locked femtosecond laser is connected to the dispersive optical fiber, the mode-locked femtosecond laser is used to generate femtosecond pulses, and the dispersive optical fiber is used to expand the femtosecond pulses in the time domain.

[0011] Preferably, the programmable structured light unit comprises: an arbitrary waveform generator, an electro-optic modulator, an erbium-doped fiber laser amplifier, a first collimator and a first diffraction grating;

[0012] The RF signal output end of the mode-locked femtosecond laser is connected to the external clock channel of the arbitrary waveform generator as a trigger signal of the arbitrary waveform generator; the tail end of the dispersive optical fiber is connected to the optical signal input end of the electro-optical modulator, and the coded signal output end of the arbitrary waveform generator is connected to the electrical signal input end of the electro-optical modulator, and the electro-optical modulator is used to generate a coded structured light signal; the optical signal output end of the electro-optical modulator is connected to the erbium-doped fiber laser amplifier, and the erbium-doped fiber laser amplifier is used to power amplify the coded structured light signal; the first collimator and the first diffraction grating are sequentially arranged on the output optical path of the erbium-doped fiber laser amplifier, and the first diffraction grating is used to spatially disperse the collimated coded structured light signal.

[0013] Preferably, the programmable structured light unit adopts a sinusoidal coding or a random binary coding signal, and the code rate is an integer multiple of the laser repetition rate in the time domain stretching unit; the signal processing unit adopts an orthogonal coding signal combined with a Fourier transform recovery algorithm to restore the image, and the random binary signal adopts an orthogonal iterative tracking algorithm to restore the image.

[0014] On the other hand, the present invention provides a compressed ultrafast imaging method based on a low-pass filter, which uses the low-pass filter as a compression component for signal acquisition, filters out the high-frequency part of the sampled signal through the low-pass filter, reduces the bandwidth of the sampled signal, and realizes signal downsampling.

[0015] Preferably, a plurality of low-pass filters connected in series are used as compression components for signal acquisition.

[0016] Preferably, the low-pass filter-based compressed ultrafast imaging method comprises the following steps:

[0017] Step 1, generating a femtosecond pulse by a mode-locked femtosecond pulse laser, and expanding the femtosecond pulse in the time domain by a dispersive optical fiber;

[0018] Step 2: Connect the RF signal output end of the mode-locked femtosecond pulse laser to the external clock channel of the arbitrary waveform generator as a trigger signal of the arbitrary waveform generator; connect the tail end of the dispersive optical fiber to the optical signal input end of the electro-optic modulator, connect the coded signal output end of the arbitrary waveform generator to the electrical signal input end of the electro-optic modulator, and the output end of the electro-optic modulator outputs a coded structured optical signal;

[0019] Step 3: the encoded structured light signal is incident on a first diffraction grating, and the pulse spectrum is dispersed in the spatial domain by the first diffraction grating;

[0020] Step 4: the coded structured light signal dispersed by the first diffraction grating is focused and irradiated onto the surface of the sample to be tested after passing through the first 4f lens system and the first objective lens, and the light signal carrying the information of the sample to be tested is incident on the second diffraction grating after passing through the second objective lens and the second 4f lens system in sequence, and the light signal is compressed in the spatial domain by the second diffraction grating;

[0021] Step 5, the compressed optical signal is input to a high-speed photodetector, the high-speed photodetector captures the sampling signal, and converts the optical signal into an analog electrical signal;

[0022] Step 6: Filter out high-frequency signals in the sampled signal through the low-pass filter to reduce the bandwidth of the sampled signal, perform low sampling rate acquisition through a high-speed oscilloscope connected to the output end of the low-pass filter, and convert the analog electrical signal into a digital electrical signal by the high-speed oscilloscope, and transmit it to a signal processing unit; the signal processing unit stores and records the acquired signal, and reconstructs the sample information using a recovery algorithm.

[0023] Preferably, in the step 3, before the coded structured light signal is incident on the first diffraction grating, it also includes: amplifying and collimating the coded structured light signal in sequence through an erbium-doped fiber laser amplifier and a first collimator; in the step 5, the compressed light signal is collimated through a second collimator and then input into the high-speed photodetector.

[0024] One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

[0025] In the present invention, a low-pass filter is used as a compression component for signal acquisition, and the high-frequency part of the sampled signal is filtered out by the low-pass filter, thereby reducing the bandwidth of the sampled signal and realizing signal downsampling. That is, the present invention uses a low-pass filter to replace the dispersion optical fiber commonly used in the prior art to realize ultrafast imaging of signal compression. The present invention can compress the signal spectrum based on compression coding, thereby realizing signal downsampling by using a low-pass filter, effectively reducing system complexity and cost, and improving the signal-to-noise ratio of the restored image. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A principle block diagram of a low-pass filter-based compressed ultrafast imaging system provided by an embodiment of the present invention;

[0027] Figure 2 A schematic structural diagram of a low-pass filter-based compressed ultrafast imaging system provided in an embodiment of the present invention.

[0028] Among them, 101-mode-locked femtosecond laser, 102-dispersive optical fiber, 103-arbitrary waveform generator, 104-electro-optic modulator, 105-erbium-doped fiber laser amplifier, 106-first collimator, 107-first diffraction grating, 108-first 4f lens system, 109-first objective lens, 110-second objective lens, 111-second 4f lens system, 112-second diffraction grating, 113-second collimator, 114-high-speed photodetector, 115-low-pass filter, 116-high-speed oscilloscope, 117-computer. DETAILED DESCRIPTION

[0029] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0030] Embodiment 1:

[0031] Embodiment 1 provides a low-pass filter-based compressed ultrafast imaging system. Figure 1 and Figure 2 , including: a time domain stretching unit, a programmable structured light unit, a high-speed signal acquisition unit and a signal processing unit; wherein the high-speed signal acquisition unit includes a low-pass filter, and the low-pass filter is used as a compression component for signal acquisition to filter out the high-frequency part of the sampling signal, reduce the bandwidth of the sampling signal, and realize signal downsampling.

[0032] This system uses a dispersion device to broaden high-repetition-rate femtosecond short pulses in the time domain, encodes the broadened pulses through a coding device, performs random observations on the sample to be tested, and evenly spreads the signal spectrum on the entire frequency axis. When collecting signals, a low-pass filter is used to filter out high-frequency signals, reduce the signal bandwidth, and achieve signal compression.

[0033] For details, see Figure 2 The time-domain stretching unit includes the following devices: a mode-locked femtosecond laser 101 and a dispersive optical fiber 102. The time-domain stretching unit, as the imaging light source part of the system, stretches the femtosecond pulses with high repetition rate in the time domain through the dispersive component for the next step of structured light modulation.

[0034] The programmable structured light unit comprises the following devices: an arbitrary waveform generator 103, an electro-optic modulator 104, an erbium-doped fiber laser amplifier 105, a first collimator 106, and a first diffraction grating 107. The programmable structured light unit is used to encode the time-domain stretched optical pulses to generate structured light.

[0035] The high-speed signal acquisition unit includes the following devices: a first 4f lens system 108, a first objective lens 109, a second objective lens 110, a second 4f lens system 111, a second diffraction grating 112, a second collimator 113, a high-speed photodetector 114, a low-pass filter 115, and a high-speed oscilloscope 116. The sample to be imaged is located between the first objective lens 109 and the second objective lens 110. The high-speed signal acquisition unit is responsible for collecting and compressing the structured light signal containing sample information and converting it into an analog electrical signal. Among them, the high-speed signal acquisition unit uses the low-pass filter 115 as a compression component for system signal acquisition, and reduces the bandwidth of the detection signal through the low-pass filter 115 to achieve signal compression. That is, the high-speed signal acquisition unit captures the encoded detection signal containing sample information by the high-speed photodetector 114, and then filters out the high-frequency signal by the low-pass filter 115, thereby greatly reducing the bandwidth of the signal and achieving downsampling. In a preferred solution, the high-speed signal acquisition unit uses multiple low-pass filters 115 connected in series as compression components for signal acquisition.

[0036] The signal processing unit includes the following devices: a computer 117. The signal processing unit uses a recovery algorithm to quickly reconstruct the graphic information of the detection sample. The programmable structured light unit uses a sinusoidal coding or a random binary coding signal, and the code rate is an integer multiple of the laser repetition rate in the time domain stretching unit; the signal processing unit uses an orthogonal coding signal combined with a Fourier transform recovery algorithm to restore the image, and the random binary signal uses an orthogonal iterative tracking algorithm to restore the image.

[0037] The present invention is described below in conjunction with parameters and device models.

[0038] The mode-locked femtosecond laser 101 is a pulsed laser with a central wavelength of 1550nm, a spectrum width of 30nm, a pulse width of 100fs, and a repetition frequency of 101.7MHz; the dispersive fiber 102 is a single-mode fiber with a group velocity dispersion of 300ps / nm; the arbitrary waveform generator 103 is the M8195A of Keysight of the United States; the electro-optic modulator 104 is a 40Gbps Mach-Zehnder modulator in the 1550nm band; the erbium-doped fiber laser amplifier 105 is a working wavelength in the 1550nm band Erbium-doped fiber laser amplifier; the first collimator 106 and the second collimator 113 are selected as F260FC-1550 of Thorlabs; the first diffraction grating 107 and the second diffraction grating 112 are selected as GR25-0616 of Thorlabs; the first 4f lens system 108 and the second 4f lens system 111 are selected as LA1131-C and LA1509-C of Thorlabs; the first objective lens 109 and the second objective lens 110 are selected as Mitutoyo M Plan Apo NIR HR 50', with a magnification of 50 times; the transmission rate of the high-speed photodetector 114 is 10 Gbps; the low-pass filter 115 is selected as SLP-50+ of Mini-Circuits Company of the United States; the high-speed oscilloscope 116 is selected as DSA91304A of Keysight of the United States.

[0039] See also Figure 2The optical signal output end of the mode-locked femtosecond laser 101 is connected to the dispersive optical fiber 102, which is used to expand the laser spectrum in the time domain and realize the mapping of time domain information and frequency domain information; the RF signal output end of the mode-locked femtosecond laser 101 is connected to the external clock channel of the arbitrary waveform generator 103 as the trigger signal of the arbitrary waveform generator; the tail end of the dispersive optical fiber 102 is connected to the optical signal input end of the electro-optical modulator 104, the coded signal output end of the arbitrary waveform generator 103 is connected to the electrical signal input end of the electro-optical modulator 104, and the electro-optical modulator 104 is used to generate a coded optical signal; the electro-optical modulator 104 The optical signal output end is connected to the erbium-doped fiber laser amplifier 105, and the erbium-doped fiber laser amplifier 105 is used to amplify the power of the coded structure light signal to improve the system imaging signal-to-noise ratio; the first collimator 106 is connected to the erbium-doped fiber laser amplifier 105, and the collimated coded structure light signal is incident on the first diffraction grating 107 at a certain angle, and the first diffraction grating 107 is used to disperse the collimated coded structure light signal in space to achieve a one-to-one mapping of the frequency domain, time domain, and space domain of the optical signal. For example, the first diffraction grating 107 is placed on the first collimator at a distance d1=100mm and an angle θ1=55°. 106; the first 4f lens system 108 and the first objective lens 109 are sequentially arranged behind the first diffraction grating 107, and the first 4f lens system 108 and the first objective lens 109 are used to focus the coded structure light signal on the surface of the sample to be tested. For example, the first 4f lens system 108 is placed on the output light path of the first diffraction grating 107 at a distance d2=150mm and an angle θ2=15°, and the first objective lens 109 is arranged on the output light path of the first 4f lens system 108 at a distance d3=50mm; the optical signal carrying the information of the sample to be tested passes through the second objective lens 110 and the first objective lens 110 in sequence. After the second 4f lens system 111, the light is incident on the second diffraction grating 112 at a certain angle to compress the light pulse widened in the spatial domain. For example, the second objective lens 110 is located on the output light path of the first objective lens 109 at a distance d4=20 mm, and the second 4f lens system 111 is located on the output light path of the second objective lens 110 at a distance d5=50 mm. The signal passing through the second 4f lens system 111 is incident on the second diffraction grating 112 at an angle θ3=50° and a distance d6=100 mm. The second diffraction grating 112 is used to perform spatial domain compression on the light signal, that is, to compress the light pulse widened in the spatial domain.The compressed optical signal is collimated by the second collimator and then input into the high-speed photodetector. Specifically, the second collimator 113 is located after the second diffraction grating 112, and couples the spatial light beam into the single-mode optical fiber. For example, the second collimator 113 is located at a distance d7=20 mm on the output optical path of the second diffraction grating 112. The optical signal input end of the high-speed photodetector 114 is connected to the output end of the single-mode optical fiber to transmit the information of the sample to be tested at high speed; that is, the high-speed photodetector 114 is used to capture the sampling signal and convert the optical signal into an analog electrical signal; the low-pass filter The oscilloscope 115 is connected to the RF signal output end of the high-speed photodetector 114. The low-pass filter 115 is used to filter the high-frequency signal in the sampled signal and reduce the signal bandwidth; a signal input end of the high-speed oscilloscope 116 is connected to the output end of the low-pass filter 115. The high-speed oscilloscope 116 is used to perform low sampling rate acquisition, convert the analog electrical signal into a digital signal, and transmit it to the computer 117; the computer 117 and the high-speed oscilloscope 116 work in the same local area network, and are responsible for storing and recording the acquisition signal and reconstructing the image information using the recovery algorithm. ;

[0040] Embodiment 2:

[0041] Example 2 provides a compressed ultrafast imaging method based on a low-pass filter, which is implemented using the system provided in Example 1, and uses the low-pass filter as a compression component for signal acquisition. The high-frequency part of the sampled signal is filtered out by the low-pass filter, thereby reducing the bandwidth of the sampled signal and realizing signal downsampling.

[0042] In a preferred solution, a plurality of low-pass filters connected in series are used as compression components for signal acquisition.

[0043] Specifically, a low-pass filter-based compressed ultrafast imaging method provided in Example 2 includes the following steps:

[0044] Step 1, generating a femtosecond pulse by a mode-locked femtosecond pulse laser, and expanding the femtosecond pulse in the time domain by a dispersive optical fiber;

[0045] Step 2: Connect the RF signal output end of the mode-locked femtosecond pulse laser to the external clock channel of the arbitrary waveform generator as a trigger signal of the arbitrary waveform generator; connect the tail end of the dispersive optical fiber to the optical signal input end of the electro-optic modulator, connect the coded signal output end of the arbitrary waveform generator to the electrical signal input end of the electro-optic modulator, and the output end of the electro-optic modulator outputs a coded structured optical signal;

[0046] Step 3: the encoded structured light signal is incident on a first diffraction grating, and the pulse spectrum is dispersed in the spatial domain by the first diffraction grating;

[0047] Step 4: the coded structured light signal dispersed by the first diffraction grating is focused and irradiated onto the surface of the sample to be tested after passing through the first 4f lens system and the first objective lens, and the light signal carrying the information of the sample to be tested is incident on the second diffraction grating after passing through the second objective lens and the second 4f lens system in sequence, and the light signal is compressed in the spatial domain by the second diffraction grating;

[0048] Step 5, the compressed optical signal is input to a high-speed photodetector, the high-speed photodetector captures the sampling signal, and converts the optical signal into an analog electrical signal;

[0049] Step 6: Filter out high-frequency signals in the sampled signal through the low-pass filter to reduce the bandwidth of the sampled signal, perform low sampling rate acquisition through a high-speed oscilloscope connected to the output end of the low-pass filter, and convert the analog electrical signal into a digital electrical signal by the high-speed oscilloscope, and transmit it to a signal processing unit; the signal processing unit stores and records the acquired signal, and reconstructs the sample information using a recovery algorithm.

[0050] In addition, in the step 3, before the coded structured light signal is incident on the first diffraction grating, it may also include: amplifying and collimating the coded structured light signal in turn through an erbium-doped fiber laser amplifier and a first collimator; in the step 5, the compressed light signal may also be collimated through a second collimator and then input into the high-speed photodetector.

[0051] The embodiments of the present invention provide a low-pass filter-based compressed ultrafast imaging system and method, which at least include the following technical effects:

[0052] The present invention uses a low-pass filter to filter out the high-frequency part of the detection signal, and then uses a high-speed oscilloscope to collect the detection signal at a low sampling rate and high speed, which can effectively reduce the amount of sampled data, shorten the sampling time, and increase the signal power, and can better play the advantages of the high repetition rate of the femtosecond laser. At the same time, the compressed ultrafast imaging method based on the low-pass filter can avoid the power loss caused by the compression of the dispersion fiber, improve the signal-to-noise ratio of the image, and improve the image quality of high-speed imaging. And the compressed ultrafast imaging system provided by the present invention has a simple overall structure and has good practicality and adjustability.

[0053] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A low-pass filter-based compressed ultrafast imaging system, characterized in that: include: Time domain stretching unit, programmable structured light unit, high-speed signal acquisition unit and signal processing unit; The time domain stretching unit comprises: a mode-locked femtosecond laser and a dispersive optical fiber; the optical signal output end of the mode-locked femtosecond laser is connected to the dispersive optical fiber, the mode-locked femtosecond laser is used to generate femtosecond pulses, and the dispersive optical fiber is used to expand the femtosecond pulses in the time domain; The programmable structured light unit includes: an arbitrary waveform generator, an electro-optic modulator, an erbium-doped fiber laser amplifier, a first collimator and a first diffraction grating; the radio frequency signal output end of the mode-locked femtosecond laser is connected to the external clock channel of the arbitrary waveform generator as a trigger signal of the arbitrary waveform generator; the tail end of the dispersive optical fiber is connected to the optical signal input end of the electro-optic modulator, the coded signal output end of the arbitrary waveform generator is connected to the electrical signal input end of the electro-optic modulator, and the electro-optic modulator is used to generate a coded structured light signal; the optical signal output end of the electro-optic modulator is connected to the erbium-doped fiber laser amplifier, and the erbium-doped fiber laser amplifier is used to power amplify the coded structured light signal; the first collimator and the first diffraction grating are sequentially arranged on the output optical path of the erbium-doped fiber laser amplifier, and the first diffraction grating is used to spatially disperse the collimated coded structured light signal; The high-speed signal acquisition unit includes: a first 4f lens system, a first objective lens, a second objective lens, a second 4f lens system, a second diffraction grating, a second collimator, a high-speed photodetector, a low-pass filter and a high-speed oscilloscope; the first 4f lens system and the first objective lens are used to focus the coded structure light signal on the surface of the sample to be tested; the light signal carrying the information of the sample to be tested passes through the second objective lens and the second 4f lens system in sequence and is incident on the second diffraction grating, and the second diffraction grating is used to compress the light signal in the spatial domain; the compressed light signal is collimated by the second collimator and then input into the high-speed photodetector, and the high-speed oscilloscope is used to collect the light signal from the sample to be tested. The electrical detector is used to capture the sampling signal and convert the optical signal into an analog electrical signal; the radio frequency signal output end of the high-speed photodetector is connected to the input end of the low-pass filter, and the output end of the low-pass filter is connected to the signal input end of the high-speed oscilloscope; the low-pass filter is used as a compression component for signal acquisition to filter out the high-frequency part of the sampling signal, reduce the bandwidth of the sampling signal, and realize signal downsampling; the high-speed oscilloscope reduces the channel bandwidth of the acquisition signal to be consistent with the cutoff frequency of the low-pass filter, and the high-speed oscilloscope is used to perform low sampling rate acquisition, convert the analog electrical signal into a digital signal, and transmit it to the signal processing unit.

2. The low-pass filter-based compressed ultrafast imaging system according to claim 1, characterized in that: The high-speed signal acquisition unit uses a plurality of serially connected low-pass filters as compression components for signal acquisition.

3. The low-pass filter-based compressed ultrafast imaging system according to claim 1, characterized in that: The programmable structured light unit adopts a sinusoidal coding or a random binary coding signal, and the code rate is an integer multiple of the laser repetition rate in the time domain stretching unit; the signal processing unit adopts an orthogonal coding signal combined with a Fourier transform recovery algorithm to restore the image, and the random binary signal adopts an orthogonal iterative tracking algorithm to restore the image.

4. A compressed ultrafast imaging method based on a low-pass filter, characterized in that: The following steps are involved: Step 1, generating a femtosecond pulse by a mode-locked femtosecond pulse laser, and expanding the femtosecond pulse in the time domain by a dispersive optical fiber; Step 2, connecting the radio frequency signal output end of the mode-locked femtosecond pulse laser to the external clock channel of the arbitrary waveform generator as a trigger signal of the arbitrary waveform generator; Connecting the tail end of the dispersion optical fiber to the optical signal input end of the electro-optic modulator, connecting the coded signal output end of the arbitrary waveform generator to the electrical signal input end of the electro-optic modulator, and the output end of the electro-optic modulator outputs a coded structured optical signal; Step 3, amplifying and collimating the coded structured light signal in sequence through an erbium-doped fiber laser amplifier and a first collimator; the coded structured light signal is incident on a first diffraction grating, and the pulse spectrum is dispersed in the spatial domain through the first diffraction grating; Step 4: the coded structured light signal dispersed by the first diffraction grating is focused and irradiated onto the surface of the sample to be tested after passing through the first 4f lens system and the first objective lens, and the light signal carrying the information of the sample to be tested is incident on the second diffraction grating after passing through the second objective lens and the second 4f lens system in sequence, and the light signal is compressed in the spatial domain by the second diffraction grating; Step 5, the compressed optical signal is collimated by a second collimator and then input into a high-speed photodetector, the high-speed photodetector captures the sampling signal and converts the optical signal into an analog electrical signal; Step 6: Use the low-pass filter as a compression component for signal acquisition, filter out the high-frequency part of the sampled signal through the low-pass filter, reduce the bandwidth of the sampled signal, and achieve signal downsampling; perform low sampling rate acquisition through a high-speed oscilloscope connected to the output end of the low-pass filter, the high-speed oscilloscope converts the analog electrical signal into a digital electrical signal, and transmits it to a signal processing unit; the signal processing unit stores and records the acquired signal, and reconstructs the sample information using a recovery algorithm.

5. The low-pass filter-based compressed ultrafast imaging method according to claim 4, characterized in that: Multiple low-pass filters connected in series are used as compression components for signal acquisition.

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