Radio frequency pulse width measuring device and method based on microwave photon technology

Abstract

The invention discloses a radio frequency pulse width measuring device and method based on a microwave photon technology, belongs to the technical field of microwave photons, and solves the problem that in the prior art, an envelope detector is used for measuring radio frequency pulse parameters, and the measurement requirement for ultra-wideband radio frequency signals is difficult to meet; the advantages of ultra-wideband signal processing of the microwave photon technology are utilized, ultra-wideband radio-frequency pulse signals are processed in an optical domain through two modulation modes, and two low-frequency edge pulse signals are output through beat frequency of a photoelectric detector. The radio frequency pulse signal to be measured in the ultra-wideband frequency range is converted into the range of the low-frequency signal for acquisition and measurement, and ultra-wideband and rapid pulse width measurement of the ultra-wideband radio frequency signal can be realized without the acquisition and processing capability of the high-speed ultra-wideband radio frequency signal.

Description

Technical Field

[0001] The invention belongs to the field of microwave photon technology and relates to a radio frequency pulse width measurement device and method based on microwave photon technology. Background Art

[0002] The parameters of traditional modulated RF pulses include pulse width, rise time, fall time, etc., and their measurement method mainly relies on the envelope detector to detect the RF pulse envelope, and then perform further signal processing. For example, the invention patent with application publication number CN110620571A discloses an on-off keying demodulator applied to ultra-wideband RF receivers, which uses envelope detection for demodulation. The signal is first squared to obtain a square current, and then the current is converted into a voltage using RC as a load. At the same time, the RC circuit can be used as a low-pass filter circuit to filter out the high-frequency components of the circuit to obtain an envelope signal. RF pulse envelope detection has very high requirements on the sensitivity and linear characteristics of the detector. At the same time, the nonlinear characteristics of the detector will cause the detected waveform to be blurred, and the same signal will have significantly different measurement results when using different detectors, or even the same detector but with different sampling rates. With the continuous development of electronic systems and the continuous improvement of the ability to transmit, receive and process ultra-wideband RF signals, the operating frequency bands of electronic systems are getting higher and higher, and their operating bandwidths have gradually expanded to the millimeter wave bands. The instantaneous bandwidth has expanded to several GHz, or even 10 GHz. Ultra-wideband RF signals are posing increasing challenges to the integration and design of detection devices.

[0003] Microwave photonic technology is a cross-integration technology that transforms microwave signals into the optical domain and realizes signal control and processing through optical methods. By modulating microwave signals onto optical signals, microwave signal processing is realized in the optical domain. It has the advantages of large bandwidth, adjustable frequency band, low loss, and strong anti-electromagnetic interference ability. It is an indispensable module in the next generation of wireless communication, radar detection, satellite communication, deep space exploration, satellite payload and other electronic equipment. Microwave photonic technology can effectively meet the measurement requirements of ultra-wideband RF signal parameters. In order to meet the actual application requirements of ultra-wideband, fast speed and anti-electromagnetic interference, it is particularly important to develop a RF pulse width measurement device based on microwave photonic technology. Summary of the invention

[0004] The technical solution of the present invention is used to solve the problem that the prior art uses an envelope detector to measure radio frequency pulse parameters, but it is difficult to achieve the measurement requirement for ultra-wideband radio frequency signals.

[0005] The present invention solves the above technical problems through the following technical solutions:

[0006] A radio frequency pulse width measurement device based on microwave photon technology comprises a laser, a modulation unit and a detection unit connected in sequence; the modulation unit comprises a first optical coupler, a first radio frequency power divider, an amplitude modulator, a phase modulator, a first adjustable optical delay line, an acousto-optic frequency shifter and a second optical coupler; the input end of the first optical coupler is connected to the output end of the laser, the first output end of the first optical coupler is connected to the amplitude modulator and the first adjustable optical delay line in sequence to form a first modulation optical path, the output end of the first adjustable optical delay line is connected to the first input end of the second optical coupler, the second output end of the first optical coupler is connected to the phase modulator and the acousto-optic frequency shifter in sequence to form a second modulation optical path, the output end of the acousto-optic frequency shifter is connected to the second input end of the second optical coupler; the first output end of the first radio frequency power divider is connected to the radio frequency input end of the amplitude modulator, and the second output end of the first radio frequency power divider is connected to the radio frequency input end of the phase modulator;

[0007] The detection unit includes a third optical coupler, a first bandpass filter, a second bandpass filter, a second adjustable optical delay line, a first photodetector, a second photodetector and a second radio frequency power divider; the input end of the third optical coupler is connected to the output end of the second optical coupler, the first output end of the third optical coupler is connected to the first bandpass filter and the first photodetector in sequence to form a first detection optical path, the output end of the first photodetector is connected to the first input end of the second radio frequency power divider, the second output end of the third optical coupler is connected to the second bandpass filter, the second adjustable optical delay line and the second photodetector in sequence to form a second detection optical path, and the output end of the second photodetector is connected to the second input end of the second radio frequency power divider.

[0008] Furthermore, the first RF power divider divides the RF pulse signal to be measured into two RF signals with equal power and equal phase, and loads them onto the amplitude modulator and the phase modulator respectively, and performs amplitude modulation on the first modulation optical path and phase modulation on the second modulation optical path respectively; the optical signal after amplitude modulation includes two optical sidebands with the same phase, and the optical signal after phase modulation includes two optical sidebands with a phase difference of 180°.

[0009] Furthermore, it is characterized in that the working state of the amplitude modulator and the phase modulator can be double-sideband modulation or carrier suppression modulation.

[0010] Furthermore, the acousto-optic frequency shifter performs frequency shift modulation on the phase-modulated optical signal, and the first adjustable optical delay line delays the amplitude-modulated optical signal, so as to keep the optical path of the optical signal on the first modulated optical path and the optical path on the second modulated optical path consistent.

[0011] Furthermore, the second optical coupler combines the first modulated optical path and the second modulated optical path to output a single optical signal, and the single optical signal includes an amplitude modulated optical signal and a phase modulated optical signal.

[0012] Furthermore, the third optical coupler divides the combined output single optical signal into two optical signals with equal power, and sends them to the first detection optical path and the second detection optical path respectively.

[0013] Furthermore, the bandpass performance of the first bandpass filter and the second bandpass filter are opposite. When the first bandpass filter is an upper sideband filter, the second bandpass filter is a lower sideband filter; when the first bandpass filter is a lower sideband filter, the second bandpass filter is an upper sideband filter.

[0014] Furthermore, the second adjustable optical delay line delays the filtered optical signal, and the first detection optical path and the second detection optical path generate an optical delay difference; the first photodetector and the second photodetector beat frequency to output a low-frequency pulse signal, the frequency of the low-frequency pulse signal is the frequency shift amount of the acousto-optic frequency shifter, the low-frequency pulse signal output by the first photodetector and the low-frequency pulse signal output by the second photodetector have a phase difference of 180°, and there is a delay difference in the pulse timing, and the delay difference is adjusted by the second adjustable optical delay line.

[0015] Furthermore, the second RF power splitter combines the first detection optical path and the second detection optical path to output a single RF pulse signal, and obtains the pulse time width of the RF pulse signal to be measured through low-rate acquisition and counting.

[0016] The present invention also provides a method for measuring radio frequency pulse width based on microwave photon technology, comprising the following steps:

[0017] S100, the laser signal output by the laser is used as an optical carrier signal, and the first optical coupler divides the optical carrier signal into two optical signals with equal power, and sends them to the first modulation optical path and the second modulation optical path respectively;

[0018] S200, the first RF power divider divides the RF pulse signal to be measured into two RF signals with equal power and equal phase, and loads them to the amplitude modulator and the phase modulator respectively, and performs amplitude modulation on the first modulation optical path and phase modulation on the second modulation optical path respectively;

[0019] S300, the acousto-optic frequency shifter performs frequency shift modulation on the phase-modulated optical signal, and the first adjustable optical delay line delays the amplitude-modulated optical signal, so that the optical path lengths of the optical signals on the first modulated optical path and the second modulated optical path are kept consistent;

[0020] S400, the second optical coupler combines the first modulation optical path and the second modulation optical path to output a single optical signal, so that the single optical signal output by the modulation unit includes an amplitude modulated optical signal and a phase modulated optical signal;

[0021] S500, the third optical coupler divides the single optical signal output by the combined path into two optical signals with equal power, and sends them to the first detection optical path and the second detection optical path respectively, and the first bandpass filter and the second bandpass filter filter the optical signal, when the first bandpass filter allows the upper sideband of the optical signal to pass, the second bandpass filter allows the lower sideband of the optical signal to pass, and when the first bandpass filter allows the lower sideband of the optical signal to pass, the second bandpass filter allows the upper sideband of the optical signal to pass;

[0022] S600, the second adjustable optical delay line delays the filtered optical signal, the first detection optical path and the second detection optical path generate an optical delay difference, and the first photodetector and the second photodetector beat frequency to output a low-frequency pulse signal;

[0023] S700, the second RF power splitter combines the first detection optical path and the second detection optical path to output a single RF pulse signal, and obtains the pulse time width of the RF pulse signal to be measured through low-rate acquisition and counting.

[0024] The advantages of the present invention are as follows: the present invention utilizes the advantages of ultra-wideband signal processing of microwave photon technology, processes ultra-wideband radio frequency pulse signals in the optical domain through two modulation modes, utilizes the beat frequency of a photoelectric detector to output two low-frequency edge pulse signals, and converts the radio frequency pulse signal to be measured within the ultra-wideband frequency range to a low-frequency signal range for collection and measurement, and can realize ultra-wideband and fast pulse width measurement of ultra-wideband radio frequency signals without the need for high-speed ultra-wideband radio frequency signal collection and processing capabilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a structural diagram of a radio frequency pulse width measurement device based on microwave photon technology according to an embodiment of the present invention;

[0026] Figure 2 It is a frequency domain schematic diagram of a modulation signal of a radio frequency pulse width measurement device based on microwave photon technology according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments:

[0029] Embodiment 1

[0030] like Figure 1 As shown, specifically, a radio frequency pulse width measurement device based on microwave photon technology is disclosed, including a laser, a modulation unit and a detection unit connected in sequence;

[0031] The modulation unit includes a first optical coupler, a first radio frequency power divider, an amplitude modulator, a phase modulator, a first adjustable optical delay line, an acousto-optic frequency shifter, and a second optical coupler; the input end of the first optical coupler is connected to the output end of the laser, the first output end of the first optical coupler is connected to the amplitude modulator and the first adjustable optical delay line in sequence to form a first modulation optical path, the output end of the first adjustable optical delay line is connected to the first input end of the second optical coupler, the second output end of the first optical coupler is connected to the phase modulator and the acousto-optic frequency shifter in sequence to form a second modulation optical path, and the output end of the acousto-optic frequency shifter is connected to the second input end of the second optical coupler; the first output end of the first radio frequency power divider is connected to the radio frequency input end of the amplitude modulator, and the second output end of the first radio frequency power divider is connected to the radio frequency input end of the phase modulator;

[0032] The detection unit includes a third optical coupler, a first bandpass filter, a second bandpass filter, a second adjustable optical delay line, a first photodetector, a second photodetector and a second radio frequency power divider; the input end of the third optical coupler is connected to the output end of the second optical coupler, the first output end of the third optical coupler is connected to the first bandpass filter and the first photodetector in sequence to form a first detection optical path, the output end of the first photodetector is connected to the first input end of the second radio frequency power divider, the second output end of the third optical coupler is connected to the second bandpass filter, the second adjustable optical delay line and the second photodetector in sequence to form a second detection optical path, and the output end of the second photodetector is connected to the second input end of the second radio frequency power divider.

[0033] The laser signal output by the laser is used as an optical carrier signal, and the first optical coupler divides the optical carrier signal into two optical signals with equal power, and sends them to the first modulation optical path and the second modulation optical path respectively;

[0034] The first RF power divider divides the RF pulse signal to be measured into two RF signals with equal power and equal phase, and loads them to the amplitude modulator and the phase modulator respectively, and performs amplitude modulation on the first modulation optical path and phase modulation on the second modulation optical path respectively; the optical signal after amplitude modulation includes two optical sidebands with the same phase, and the optical signal after phase modulation includes two optical sidebands with a phase difference of 180°, such as Figure 2 shown.

[0035] The working state of the amplitude modulator and the phase modulator can be double-sideband modulation or carrier suppression modulation. Double-sideband modulation can make the spectrum of the optical signal produce symmetrical frequency bands on both sides of the carrier frequency through the interaction of the carrier signal and the modulation signal. The modulated optical signal contains the original optical carrier signal frequency and two sideband frequencies. However, the spectrum of the optical signal after carrier suppression modulation does not contain the original optical carrier signal frequency, but only contains two sideband frequencies, without the need for a central carrier component.

[0036] The acousto-optic frequency shifter performs frequency shift modulation on the phase-modulated optical signal. The frequency shift amount is considered based on the bandwidth of the photodetector and the sampling rate of the back end of the measuring device system, and is used to realize heterodyne detection to avoid homodyne detection without frequency shift being easily affected by the output zero-frequency component. Figure 2 As shown, in this embodiment, the selectable frequency shift amount is from tens of MHz to hundreds of MHz.

[0037] The first adjustable optical delay line delays the amplitude modulated optical signal to keep the optical path of the optical signal on the first modulated optical path consistent with that on the second modulated optical path.

[0038] The second optical coupler combines the first modulated optical path and the second modulated optical path to output a single optical signal, so that the single optical signal output by the modulation unit includes an optical signal that has been amplitude modulated and an optical signal that has been phase modulated. The present invention combines two optical signals that have been amplitude modulated and phase modulated so that the single optical signal output by the modulation unit includes the effects of the two modulation signals at the same time, so that each optical signal in the detection unit has the comprehensive characteristics of the two modulation signals, and the modulation effects brought by different modulation signals can be effectively tested and utilized.

[0039] The third optical coupler divides the single optical signal output by the combined path into two optical signals of equal power, and sends them to the first detection optical path and the second detection optical path respectively; the first bandpass filter and the second bandpass filter filter the optical signal. Since the output values ​​of the two sidebands will be different after interference, their superposition will affect the threshold judgment of the output optical power value in the later stage, and it is impossible to judge whether the frequency band of the signal falls within the corresponding frequency range. Therefore, the passband position of the bandpass filter requires that the modulated optical signal can only allow a single optical sideband to pass;

[0040] The first bandpass filter and the second bandpass filter have opposite bandpass properties, such as Figure 2 As shown, when the first bandpass filter is an upper sideband filter, the second bandpass filter is a lower sideband filter; when the first bandpass filter is a lower sideband filter, the second bandpass filter is an upper sideband filter, so that the signals filtered out by the upper and lower channels are different, so that the opposite phases can be offset when the subsequent photoelectric detector beats the output.

[0041] The second adjustable optical delay line delays the filtered optical signal, and the first detection optical path and the second detection optical path generate an optical delay difference. The first photodetector and the second photodetector beat frequency to output a low-frequency pulse signal, the frequency of the low-frequency pulse signal is the frequency shift amount of the acousto-optic frequency shifter, the low-frequency pulse signal output by the first photodetector and the low-frequency pulse signal output by the second photodetector have a phase difference of 180°, and there is a delay difference in the pulse timing, and the delay difference can be adjusted by the second adjustable optical delay line. Since there are two optical signals of modulation modes in the optical signal output by the modulation unit, the RF pulse signal to be measured can be converted into a low-frequency pulse signal by using the beat frequency output method, and the RF pulse signal to be measured within the ultra-wideband frequency range is converted to a low-frequency range for collection and measurement, without the need for high-speed ultra-wideband RF signal collection and processing, which can significantly reduce the amount of system equipment and power consumption, and has lower requirements for signal collection and data processing. At the same time, the frequency measuring device has the characteristics of instantaneous operation and can measure the frequency of the RF signal in real time.

[0042] The second RF power divider combines the first detection optical path and the second detection optical path to output a single RF pulse signal. Since the two low-frequency pulse signals are in opposite directions and have a delay difference, two narrow RF pulses are formed after superposition and combination. The timing position of the pulses corresponds to the leading and trailing edges of the RF pulse signal to be measured. At this time, the carrier frequency of the pulse is a low-frequency signal. The pulse time width of the RF pulse signal to be measured is then obtained through low-rate acquisition and counting.

[0043] The measuring device provided by the present invention can be implemented on a chip by means of photon integration, so as to better meet the practical application requirements of ultra-wideband, anti-electromagnetic interference and rapid response.

[0044] The present invention utilizes the advantages of ultra-wideband signal processing of microwave photon technology, processes the ultra-wideband radio frequency pulse signal in the optical domain through two modulation modes, utilizes the beat frequency of the photoelectric detector to output two low-frequency edge pulse signals, and converts the radio frequency pulse signal to be measured within the ultra-wideband frequency range to the range of the low-frequency signal for collection and measurement. The ultra-wideband and fast pulse width measurement of the ultra-wideband radio frequency signal can be realized without the need for high-speed ultra-wideband radio frequency signal collection and processing capabilities.

[0045] The present invention also provides a method for measuring radio frequency pulse width based on microwave photon technology, comprising the following steps:

[0046] S100, the laser signal output by the laser is used as an optical carrier signal, and the first optical coupler divides the optical carrier signal into two optical signals with equal power, and sends them to the first modulation optical path and the second modulation optical path respectively;

[0047] S200, the first RF power divider divides the RF pulse signal to be measured into two RF signals with equal power and equal phase, and loads them to the amplitude modulator and the phase modulator respectively, and performs amplitude modulation on the first modulation optical path and phase modulation on the second modulation optical path respectively;

[0048] S300, the acousto-optic frequency shifter performs frequency shift modulation on the phase-modulated optical signal, and the first adjustable optical delay line delays the amplitude-modulated optical signal, so that the optical path lengths of the optical signals on the first modulated optical path and the second modulated optical path are kept consistent;

[0049] S400, the second optical coupler combines the first modulation optical path and the second modulation optical path to output a single optical signal, so that the single optical signal output by the modulation unit includes an amplitude modulated optical signal and a phase modulated optical signal;

[0050] S500, the third optical coupler divides the single optical signal output by the combined path into two optical signals with equal power, and sends them to the first detection optical path and the second detection optical path respectively, and the first bandpass filter and the second bandpass filter filter the optical signal, when the first bandpass filter allows the upper sideband of the optical signal to pass, the second bandpass filter allows the lower sideband of the optical signal to pass, and when the first bandpass filter allows the lower sideband of the optical signal to pass, the second bandpass filter allows the upper sideband of the optical signal to pass;

[0051] S600, the second adjustable optical delay line delays the filtered optical signal, the first detection optical path and the second detection optical path generate an optical delay difference, and the first photodetector and the second photodetector beat frequency to output a low-frequency pulse signal;

[0052] S700, the second RF power splitter combines the first detection optical path and the second detection optical path to output a single RF pulse signal, and obtains the pulse time width of the RF pulse signal to be measured through low-rate acquisition and counting.

[0053] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A radio frequency pulse width measurement device based on microwave photon technology, characterized in that: It comprises a laser, a modulation unit and a detection unit connected in sequence; the modulation unit comprises a first optical coupler, a first radio frequency power divider, an amplitude modulator, a phase modulator, a first adjustable optical delay line, an acousto-optic frequency shifter and a second optical coupler; the input end of the first optical coupler is connected to the output end of the laser, the first output end of the first optical coupler is connected to the amplitude modulator and the first adjustable optical delay line in sequence to form a first modulation optical path, the output end of the first adjustable optical delay line is connected to the first input end of the second optical coupler, the second output end of the first optical coupler is connected to the phase modulator and the acousto-optic frequency shifter in sequence to form a second modulation optical path, and the output end of the acousto-optic frequency shifter is connected to the second input end of the second optical coupler; the first output end of the first radio frequency power divider is connected to the radio frequency input end of the amplitude modulator, and the second output end of the first radio frequency power divider is connected to the radio frequency input end of the phase modulator; The detection unit includes a third optical coupler, a first bandpass filter, a second bandpass filter, a second adjustable optical delay line, a first photodetector, a second photodetector and a second radio frequency power divider; the input end of the third optical coupler is connected to the output end of the second optical coupler, the first output end of the third optical coupler is connected to the first bandpass filter and the first photodetector in sequence to form a first detection optical path, the output end of the first photodetector is connected to the first input end of the second radio frequency power divider, the second output end of the third optical coupler is connected to the second bandpass filter, the second adjustable optical delay line and the second photodetector in sequence to form a second detection optical path, and the output end of the second photodetector is connected to the second input end of the second radio frequency power divider.

2. The radio frequency pulse width measurement device based on microwave photon technology according to claim 1, characterized in that: The first RF power divider divides the RF pulse signal to be measured into two RF signals with equal power and equal phase, and loads them onto the amplitude modulator and the phase modulator respectively, and performs amplitude modulation on the first modulation optical path and phase modulation on the second modulation optical path respectively; the optical signal after amplitude modulation includes two optical sidebands with the same phase, and the optical signal after phase modulation includes two optical sidebands with a phase difference of 180°.

3. The radio frequency pulse width measurement device based on microwave photon technology according to claim 2, characterized in that: The working state of the amplitude modulator and the phase modulator can be double sideband modulation or carrier suppression modulation.

4. The radio frequency pulse width measurement device based on microwave photon technology according to claim 2, characterized in that: The acousto-optic frequency shifter performs frequency shift modulation on the phase-modulated optical signal, and the first adjustable optical delay line delays the amplitude-modulated optical signal, so as to keep the optical path of the optical signal on the first modulated optical path consistent with that on the second modulated optical path.

5. The radio frequency pulse width measurement device based on microwave photon technology according to claim 4 is characterized in that: The second optical coupler combines the first modulated optical path and the second modulated optical path to output a single optical signal, where the single optical signal includes an amplitude modulated optical signal and a phase modulated optical signal.

6. The radio frequency pulse width measurement device based on microwave photon technology according to claim 5, characterized in that: The third optical coupler divides the combined output single optical signal into two optical signals with equal power, and sends them to the first detection optical path and the second detection optical path respectively.

7. The radio frequency pulse width measurement device based on microwave photon technology according to claim 6, characterized in that: The first bandpass filter and the second bandpass filter have opposite bandpass performances. When the first bandpass filter is an upper sideband filter, the second bandpass filter is a lower sideband filter; when the first bandpass filter is a lower sideband filter, the second bandpass filter is an upper sideband filter.

8. The radio frequency pulse width measurement device based on microwave photon technology according to claim 7, characterized in that: The second adjustable optical delay line delays the filtered optical signal, and the first detection optical path and the second detection optical path generate an optical delay difference; the first photodetector and the second photodetector beat frequency to output a low-frequency pulse signal, the frequency of the low-frequency pulse signal is the frequency shift amount of the acousto-optic frequency shifter, the low-frequency pulse signal output by the first photodetector and the low-frequency pulse signal output by the second photodetector have a phase difference of 180°, and there is a delay difference in the pulse timing, and the delay difference is adjusted by the second adjustable optical delay line.

9. The radio frequency pulse width measurement device based on microwave photon technology according to claim 8, characterized in that: The second RF power divider combines the first detection optical path and the second detection optical path to output a single RF pulse signal, and obtains the pulse time width of the RF pulse signal to be measured through low-rate acquisition and counting.

10. The method for measuring radio frequency pulse width based on microwave photon technology according to any one of claims 1 to 9, characterized in that: The following steps are involved: S100, the laser signal output by the laser is used as an optical carrier signal, and the first optical coupler divides the optical carrier signal into two optical signals with equal power, and sends them to the first modulation optical path and the second modulation optical path respectively; S200, the first RF power divider divides the RF pulse signal to be measured into two RF signals with equal power and equal phase, and loads them to the amplitude modulator and the phase modulator respectively, and performs amplitude modulation on the first modulation optical path and phase modulation on the second modulation optical path respectively; S300, the acousto-optic frequency shifter performs frequency shift modulation on the phase-modulated optical signal, and the first adjustable optical delay line delays the amplitude-modulated optical signal, so that the optical path lengths of the optical signals on the first modulated optical path and the second modulated optical path are kept consistent; S400, the second optical coupler combines the first modulation optical path and the second modulation optical path to output a single optical signal, so that the single optical signal output by the modulation unit includes an amplitude modulated optical signal and a phase modulated optical signal; S500, the third optical coupler divides the single optical signal output by the combined path into two optical signals with equal power, and sends them to the first detection optical path and the second detection optical path respectively, and the first bandpass filter and the second bandpass filter filter the optical signal, when the first bandpass filter allows the upper sideband of the optical signal to pass, the second bandpass filter allows the lower sideband of the optical signal to pass, and when the first bandpass filter allows the lower sideband of the optical signal to pass, the second bandpass filter allows the upper sideband of the optical signal to pass; S600, the second adjustable optical delay line delays the filtered optical signal, the first detection optical path and the second detection optical path generate an optical delay difference, and the first photodetector and the second photodetector beat frequency to output a low-frequency pulse signal; S700, the second RF power splitter combines the first detection optical path and the second detection optical path to output a single RF pulse signal, and obtains the pulse time width of the RF pulse signal to be measured through low-rate acquisition and counting.

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