Instantaneous microwave frequency measuring system and measuring method

Abstract

The invention relates to an instantaneous microwave frequency measuring system and measuring method. A laser of the measuring system is connected with a dual-polarization dual-drive electro-optical modulator through an optical fiber, and two output ends of an electric power divider are respectively connected with a radio frequency input port of a dual-drive electro-optical modulator in the dual-polarization dual-drive electro-optical modulator through a 90-degree bridge coupler; an optical carrier output end of the dual-polarization dual-drive electro-optical modulator is connected with an optical wave trap, an output end of the optical wave trap is connected with a polarization controller, an output end of the polarization controller is connected with an erbium-doped optical fiber amplifier, and an output end of the erbium-doped optical fiber amplifier is connected with a polarization beam splitter. Two output ends of the polarization beam splitter are respectively connected with a first instantaneous light frequency measurement module and a second instantaneous light frequency measurement module, the two instantaneous light frequency measurement modules are connected with a signal processing system, and the signal processing system calculates and processes output results of the two measurement modules to obtain an input microwave frequency. The measurement system is high in measurement precision and high in amplitude noise resistance, and synchronous high-speed instantaneous measurement can be realized.

Description

Technical Field

[0001] This invention relates to a microwave frequency measurement method, specifically an instantaneous microwave frequency measurement system and method. Background Technology

[0002] Microwave frequency measurement technology, as a core foundation of modern electronic systems, has wide applications in radar detection, 5G and 6G communications, electronic warfare, and radio frequency identification. With the continuous development of millimeter-wave communication and phased-array radar technologies, the requirements for the accuracy, range, and real-time performance of microwave signal frequency measurement are becoming increasingly stringent. Traditional electronic methods are limited by the bandwidth of electronic equipment and electromagnetic interference (EMI), making it difficult to meet the demands of modern applications. Microwave photonics technology, with its advantages of wide bandwidth, low loss, resistance to electromagnetic interference, and ease of integration, has become an ideal method for solving these problems.

[0003] The existing methods for generating and measuring frequency-modulated signals based on microwave photonics technology mainly include the following: 1. Frequency-Power Mapping Method: This method, as a microwave instantaneous frequency measurement technique, essentially achieves electro / optical power mapping by utilizing dispersive media, optical filters, microwave filter responses, or polarization control. It employs the construction of an amplitude comparison function (ACF) to instantaneously identify the RF signal. This method has a limited power measurement range, and the ACF slope is not constant, causing the system's measurement resolution to vary depending on the input RF signal frequency. Although this method offers very fast measurement speeds, its measurement resolution and error are difficult to achieve at the MHz level.

[0004] 2. Frequency-Time Mapping Method: This method linearly maps the spectral information of the input signal to the time domain using optical means. Its core principle is to utilize a dispersive medium or periodically modulated optical signal to extend different frequency components along the time axis in a specific pattern, thereby directly reflecting the spectral characteristics through the time-domain waveform. The measurement speed of this method is limited by the scanning rate of the laser.

[0005] 3. Frequency-space mapping method: This method uses specific optical components, such as arrayed waveguide gratings (AWG), fiber Bragg gratings (FBG), or optical frequency combs (OFC), to map the frequency information of microwave signals onto spatial locations, thereby achieving frequency-to-space conversion. This method can achieve instantaneous measurement of multi-tone signals, but its measurement accuracy and resolution are still relatively low.

[0006] 4. A frequency-phase mapping-based instantaneous microwave frequency measurement method. This method uses a square wave signal to control the operating point of a Mach-Zehnder modulator, and simultaneously uses an optical filter to filter the modulated optical signal, making the carrier wave the dominant frequency component at high levels and the positive first-order sideband the dominant frequency component at low levels. By calculating the phase difference between the carrier wave and the positive first-order sideband, different input RF signals are calibrated with their corresponding phase differences, and the measured RF signal input to the Mach-Zehnder modulator is calculated. Because this measurement method uses a square wave to switch the optical signal input to the optical frequency demodulation module, it is difficult to eliminate the measurement influence caused by the frequency jitter of the laser itself. Summary of the Invention

[0007] The purpose of this invention is to provide an instantaneous microwave frequency measurement system and method to solve the problem of large measurement errors caused by laser jitter in existing instantaneous microwave frequency measurement methods based on frequency-phase mapping.

[0008] The objective of this invention is achieved as follows: A transient microwave frequency measurement system, comprising: The laser's output is connected to the input of a dual-polarization dual-drive electro-optic modulator via an optical fiber, which is used to provide an optical carrier signal for the system. The power divider has an input terminal for connecting to a detection radar that captures transient microwave signals from the outside world, and two output terminals for connecting to a first 90° bridge coupler and a second 90° bridge coupler. The power divider is used to transmit the transient microwave signals captured by the detection radar to a dual-polarization dual-drive electro-optic modulator through the two 90° bridge couplers. The first 90° bridge coupler has its input end connected to a power divider, and its two output ends are each connected to an RF input end of the first dual-drive electro-optic modulator in the first branch of the dual-polarization dual-drive electro-optic modulator, which is used to load the instantaneous microwave signal onto the optical carrier signal modulated by the first branch. The second 90° bridge coupler has its input end connected to the power divider, and its two output ends are each connected to an RF input end of the second dual-drive electro-optic modulator in the second branch of the dual-polarization dual-drive electro-optic modulator. It is used to adjust the instantaneous microwave signal into an RF signal with a 90° phase difference and then load it onto the optical carrier signal modulated by the second branch. A dual-polarization dual-drive electro-optic modulator includes a first branch operating in the X-polarization state, a second branch operating in the Y-polarization state, and a polarization combiner connected to the ends of both branches. The RF input terminal of the dual-drive electro-optic modulator in the first branch is connected to the output terminal of a first 90° bridge coupler, and the RF input terminal of the dual-drive electro-optic modulator in the second branch is connected to the output terminal of a second 90° bridge coupler. The output terminal of the polarization combiner is externally connected to the input terminal of an optical notch filter. The dual-polarization dual-drive electro-optic modulator is used to load the RF signals with a 90° phase difference output from the two 90° bridge couplers onto the optical carrier signals modulated by the two branches respectively, so as to perform single-sideband modulation on the input optical carrier signals, thereby generating a positive first-order single-sideband modulation signal in the first branch and a negative first-order single-sideband modulation signal in the second branch. An optical notch filter, with its input end connected to a polarization beam combiner and its output end connected to a polarization controller, is used to suppress the power of the optical carrier modulation signal loaded with radio frequency signal output from a dual-polarization dual-drive electro-optic modulator, so that the positive first-order sideband and the negative first-order sideband become the main frequency components of the single-sideband modulation signal. The polarization controller, whose input is connected to an optical notch filter and whose output is connected to an erbium-doped fiber amplifier, is used to adjust the polarization state of the optical carrier modulation signal output by the optical notch filter so that it is consistent with the polarization state of the optical carrier modulation signal output by the dual-polarization dual-drive electro-optic modulator. An erbium-doped fiber amplifier, with its input end connected to a polarization controller and its output end connected to a polarization beam splitter, is used to amplify the power of the optical carrier modulation signal output by the polarization controller. A polarization beam splitter has its input end connected to an erbium-doped fiber amplifier, its X-polarized light output end connected to a first instantaneous optical frequency measurement module, and its Y-polarized light output end connected to a second instantaneous optical frequency measurement module. The polarization beam splitter is used to orthogonally separate the optical carrier modulation signal output from the erbium-doped fiber amplifier into X-polarized and Y-polarized states. The upper sideband modulated optical carrier modulation signal is output through the X-polarized light output end, and the lower sideband modulated optical carrier modulation signal is output through the Y-polarized light output end. The first instantaneous optical frequency measurement module has its input end connected to a polarization beam splitter and its output end connected to a signal processing system. It is used to measure the instantaneous frequency of the positive first-order single-sideband modulation signal of the upper sideband modulated optical carrier modulation signal. The second instantaneous optical frequency measurement module, with its input connected to a polarization beam splitter and its output connected to a signal processing system, is used to measure the instantaneous frequency of the negative first-order single-sideband modulated signal of the lower sideband modulated optical carrier modulation signal; and The signal processing system is connected to the first instantaneous optical frequency measurement module and the second instantaneous optical frequency measurement module, respectively. It is used to receive the measurement results of the instantaneous frequency of the positive first-order single-sideband modulated signal by the first instantaneous optical frequency measurement module and the measurement results of the instantaneous frequency of the negative first-order single-sideband modulated signal by the second instantaneous optical frequency measurement module, and thereby calculate the frequency of the instantaneous microwave signal captured by the detection radar.

[0009] Furthermore, a first dual-drive electro-optic modulator operating in the X-polarization state is connected in the first branch of the dual-polarization Mach-Zehnder modulator, and a second dual-drive electro-optic modulator operating in the Y-polarization state and a third 90° polarization rotator are connected in series in the second branch. The two branches operate in orthogonal polarization states. The end of the first branch is connected to the X-polarization state light input terminal of the polarization beam combiner, and the end of the second branch is connected to the Y-polarization state light input terminal of the polarization beam combiner.

[0010] Furthermore, the first instantaneous light frequency measurement module includes: The first optical circulator has an input terminal connected to a polarization beam splitter, an input / output terminal connected to a first 3×3 coupler module, and an output terminal connected to a first photodetector. It is used to transmit the upper sideband modulated optical carrier modulation signal to the first 3×3 coupler module and output the optical signal fed back by the first 3×3 coupler module to the first photodetector. The first 3×3 coupler module has its input / output terminals connected to the input / output terminals of the first optical circulator, its first output terminal connected to the second photodetector, and its second output terminal connected to the third photodetector. It is used to map the upper sideband modulated optical carrier modulation signal into an optical signal carrying corresponding phase information. The first photodetector has its input end connected to the first optical circulator and its output end connected to the signal processing system, and is used to convert the optical signal carrying the corresponding phase information into an electrical signal that can be processed by the signal processing system. The second photodetector, whose input is connected to the first 3×3 coupler module and whose output is connected to the signal processing system, is used to convert the optical signal carrying corresponding phase information into an electrical signal that can be processed by the signal processing system; and The third photodetector has its input end connected to the first 3×3 coupler module and its output end connected to the signal processing system. It is used to convert the optical signal carrying the corresponding phase information into an electrical signal that can be processed by the signal processing system.

[0011] Furthermore, the second instantaneous light frequency measurement module includes: The second optical circulator has its input end connected to a polarization beam splitter, its input / output end connected to a second 3×3 coupler module, and its output end connected to a fifth photodetector. It is used to transmit the lower sideband modulated optical carrier modulation signal to the second 3×3 coupler module and output the optical signal fed back by the second 3×3 coupler module to the fifth photodetector. The second 3×3 coupler module has its input / output terminals connected to the second optical circulator, its first output terminal connected to the sixth photodetector, and its second output terminal connected to the seventh photodetector. It is used to map the lower sideband modulated optical carrier modulation signal into an optical signal carrying corresponding phase information. The fifth photodetector has its input end connected to the second optical circulator and its output end connected to the signal processing system. It is used to convert the optical signal carrying the corresponding phase information into an electrical signal that can be processed by the signal processing system. The sixth photodetector, whose input is connected to the second 3×3 coupler module and whose output is connected to the signal processing system, is used to convert the optical signal carrying corresponding phase information into an electrical signal that can be processed by the signal processing system; and The seventh photodetector has its input end connected to the second 3×3 coupler module and its output end connected to the signal processing system. It is used to convert the optical signal carrying the corresponding phase information into an electrical signal that can be processed by the signal processing system.

[0012] The structures of the two instantaneous light frequency measurement modules can also take other forms. The following detailed explanation uses the first instantaneous light frequency measurement module as an example. The structure of the second instantaneous light frequency measurement module is the same as that of the first instantaneous light frequency measurement module.

[0013] The first instantaneous optical frequency measurement module includes, in sequence, a first polarized beam shifter, a first 90° polarization rotator, a first polarizer, a first optical differential delay element, a first lens, and a first unpolarized beam splitter. The first polarized beam shifter is used to shift the first beam and the second beam, which have orthogonal polarization components. The first 90° polarization rotator and the first polarizer are used to make the two beams have the same polarization state. The first optical differential delay element is used to generate an optical delay between the two beams. The first unpolarized beam splitter splits the received light into two mutually perpendicular beams. One output of the first unpolarized beam splitter is connected to a first Wollaston prism, and its other output is connected to a second Wollaston prism after passing through a first quarter-wave plate. Both Wollaston prisms are used to split one beam into two beams with orthogonal polarization components. The two outputs of the first Wollaston prism are connected to a first photodetector and a second photodetector, respectively. The two outputs of the second Wollaston prism are connected to a third photodetector and a fourth photodetector, respectively. All four photodetectors are connected to a signal processing system.

[0014] In the microwave frequency measurement system of this invention, a laser is connected to the optical carrier input of a dual-polarization dual-drive electro-optic modulator via an optical fiber. The instantaneous microwave signal captured by the detection radar is connected to the RF input ports of the first and second branches of the dual-polarization dual-drive electro-optic modulator via a power divider and two connected 90° bridge couplers. The optical carrier output of the dual-polarization dual-drive electro-optic modulator is connected to the input of an optical notch filter, the output of the optical notch filter is connected to the input of a polarization controller, the output of the polarization controller is connected to the input of an erbium-doped fiber amplifier, the output of the erbium-doped fiber amplifier is connected to the input of a polarization beam splitter, the two outputs of the polarization beam splitter are respectively connected to a first instantaneous optical frequency measurement module and a second instantaneous optical frequency measurement module, and the outputs of the two instantaneous optical frequency measurement modules are connected to the input of a signal processing system. The signal processing system calculates and processes the outputs of the two measurement modules to obtain the frequency of the captured instantaneous microwave signal.

[0015] The measurement system of this invention mainly measures the positive first-order single-sideband modulation signal of the first branch and the negative first-order single-sideband modulation signal of the second branch. Under this modulation method, the signal power of the second highest frequency component is lower than that of the positive and negative first-order sidebands, thereby making the positive and negative first-order sidebands the dominant frequency components of the single-sideband modulation signal.

[0016] When the positive first-order single-sideband modulated signal of the first branch is input to the photofrequency measurement module at the first instant, the corresponding frequency value is obtained. for: (1) When the negative first-order single-sideband modulated signal of the second branch is input to the second instantaneous photofrequency measurement module, the corresponding frequency value is obtained. for: (2) According to formulas (1) and (2), it can be seen that the frequency values ​​calculated by the instantaneous photofrequency measurement modules of the first and second branches are... and Taking the difference yields: (3) From formulas (1) and (2), it can be seen that when the laser's own frequency fluctuates, the frequency values ​​calculated by the first and second branches... The frequency will change, increasing or decreasing simultaneously. Since the measurement system of this invention is composed of positive first-order and negative first-order single-sideband signals modulated by the first and second branch dual-drive electro-optic modulators respectively, and then separated by the polarization beam splitter, the two single-sideband modulated signals are simultaneously entered into two instantaneous optical frequency measurement modules. Therefore, when the frequency of the input radio frequency signal is calculated using formula (3), the difference between the frequencies of the first and second branches will cancel the frequency jitter of the laser itself, thereby reducing the calculation error caused by the frequency jitter of the laser itself.

[0017] Therefore, the condition for the instantaneous microwave frequency measurement system of the present invention to realize microwave signal measurement is that the power of the positive first-order sideband of the first branch and the negative first-order sideband of the second branch is greater than the optical carrier signal, so that the positive first-order sideband and the negative first-order sideband become the dominant frequency components.

[0018] The frequency measurement range of the measurement system of the present invention mainly depends on the optical frequency range of the instantaneous optical frequency measurement module. By changing the optical frequency measurement range of the instantaneous optical frequency measurement module, the measurement requirements of different frequency bands can be adapted without replacing the radio frequency devices, thus giving the system excellent flexibility.

[0019] The measurement system of this invention benefits from a synchronous optical frequency differential detection scheme based on a high-resolution optical frequency measurement module. This scheme has extremely high frequency resolution, resulting in high frequency information resolution and high measurement accuracy. Simultaneously, the measurement results are insensitive to amplitude noise such as laser power fluctuations and modulator bias drift, and the differential detection technology effectively suppresses the adverse effects of laser output frequency jitter on the measurement results, significantly enhancing the system's resistance to amplitude noise. The measurement system of this invention achieves the separation and synchronous parallel processing of X and Y polarization signals through a polarization beam splitter. The signal processing system performs real-time differential calculations on the two frequency values, thereby realizing high-speed instantaneous measurement of the captured microwave signal.

[0020] The objective of this invention can also be achieved in the following ways: A method for instantaneous microwave frequency measurement includes the following steps: S1. Set up the instantaneous microwave frequency measurement system of the present invention.

[0021] S2. The laser transmits an optical carrier signal to the dual-polarization dual-drive electro-optic modulator. The power divider transmits the external radio frequency signal from the detection radar to the dual-polarization dual-drive electro-optic modulator through two 90° bridge couplers. The first 90° bridge coupler loads the captured external radio frequency signal onto the optical carrier signal modulated by the first branch for upper sideband modulation. The second 90° bridge coupler adjusts the captured external radio frequency signal to a radio frequency signal with a 90° phase difference and loads it onto the optical carrier signal modulated by the second branch for lower sideband modulation. The dual-polarization dual-drive electro-optic modulator generates a positive first-order single-sideband modulation signal in the first branch and a negative first-order single-sideband modulation signal in the second branch through single-side modulation of the two branches.

[0022] S3. The optical notch filter suppresses the power of the optical carrier modulation signal loaded with radio frequency signal output from the dual-polarization dual-drive electro-optic modulator, so that the positive first-order sideband and the negative first-order sideband become the main frequency components of the single-sideband modulation signal.

[0023] S4. The polarization controller adjusts the polarization state of the optical carrier modulation signal output by the optical notch filter to make it consistent with the polarization state of the optical carrier modulation signal output by the dual-polarization dual-drive electro-optic modulator.

[0024] S5. The erbium-doped fiber amplifier amplifies the optical signal output by the polarization controller. The polarization beam splitter orthogonally separates the optical carrier modulation signal output by the erbium-doped fiber amplifier into X-polarization and Y-polarization states, obtaining an upper sideband modulated optical carrier modulation signal and a lower sideband modulated optical carrier modulation signal. The upper sideband modulated optical carrier modulation signal is output to the first instantaneous optical frequency measurement module through the X-polarization state optical output terminal, and the lower sideband modulated optical carrier modulation signal is output to the second instantaneous optical frequency measurement module through the Y-polarization state optical output terminal.

[0025] S6. The first instantaneous optical frequency measurement module measures the instantaneous frequency of the positive first-order sideband of the upper sideband modulated optical carrier signal and inputs the measurement result into the signal processing system; the second instantaneous optical frequency measurement module measures the instantaneous frequency of the negative first-order sideband of the lower sideband modulated optical carrier signal and inputs the measurement result into the signal processing system.

[0026] S7. The signal processing system calculates and processes the received measurement results to obtain the frequency of the captured external radio frequency signal.

[0027] The instantaneous microwave frequency measurement method of this invention is characterized by the elimination of the need for a frequency sweep source, enabling synchronous and instantaneous acquisition of the RF signal frequency value of the input system. Furthermore, it can offset frequency jitter introduced by the laser, thereby reducing its impact on measurement accuracy. The microwave frequency measurement range is the same as that of the instantaneous microwave frequency measurement module. This invention provides high-quality microwave frequency measurement for radar countermeasures or military communication systems. Attached Figure Description

[0028] Figure 1 This is a system block diagram of the instantaneous microwave frequency measurement system of the present invention.

[0029] Figure 2 This is a system block diagram of Embodiment 1.

[0030] Figure 3 This is a system block diagram of Embodiment 2.

[0031] Figure 4 These are schematic diagrams of the first and second branch single-sideband modulation; where (a) is the spectrum output of the first branch when it is at the quadrature operating point, (b) is the spectrum output of the second branch when it is at the quadrature operating point, (c) is a schematic diagram of the positive first-order single-sideband modulation signal of the first branch, and (d) is a schematic diagram of the negative first-order single-sideband modulation signal of the second branch.

[0032] Figure 5 This is a schematic diagram of frequency jitter cancellation between the first and second branches.

[0033] In the diagram: 1. Laser; 2. Dual-polarization dual-drive electro-optic modulator; 3. Power divider; 4. Second 90° bridge coupler; 5. First 90° bridge coupler; 6. Optical notch filter; 7. Polarization controller; 8. Erbium-doped fiber amplifier; 9. Polarization beam splitter; 10. First instantaneous optical frequency measurement module; 10-1. First optical circulator; 10-2. First 3×3 coupler module; 10-3. First photodetector; 10-4. Second photodetector; 10-5. Third photodetector; 10-6. First polarization beam shifter; 10-7. First 90° polarization rotator; 10-8. First polarizer; 10-9. First optical differential delay element; 10-10. First lens; 10-11. First unpolarized beam splitter; 10-12. First Wollaston prism; 10-13. First quarter-wave plate; 10-14. Second Wollaston prism. 10-15, Fourth photodetector; 11, Second instantaneous optical frequency measurement module; 11-1, Second optical circulator; 11-2, Second 3×3 coupler module; 11-3, Fifth photodetector; 11-4, Sixth photodetector; 11-5, Seventh photodetector; 11-6, Second polarization beam shifter; 11-7, Second 90° polarization rotator; 11-8, Second polarizer; 11-9, Second optical differential delay element; 11-10, Second lens; 11-11, Second unpolarized beam splitter; 11-12, Third Wollaston prism; 11-13, Second quarter-wave plate; 11-14, Fourth Wollaston prism; 11-15, Eighth photodetector; 12, Signal processing system; 21, First dual-drive electro-optic modulator; 22, Second dual-drive electro-optic modulator; 23, Third 90° polarization rotator; 24, Polarization beam combiner. Detailed Implementation

[0034] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Example 1

[0035] like Figure 1 As shown, the instantaneous microwave frequency measurement system of the present invention includes a laser 1, a dual-polarization dual-drive electro-optic modulator 2, an electrical power divider 3, two 90° bridge couplers, an optical notch filter 6, a polarization controller 7, an erbium-doped fiber amplifier 8, a polarization beam splitter 9, two instantaneous optical frequency measurement modules, and a signal processing system, etc.

[0036] The output of laser 1 is connected to the input of dual-polarization dual-drive electro-optic modulator 2 via optical fiber to provide an optical carrier signal for the system. The input of power divider 3 is connected to a detection radar to capture transient microwave signals from the outside world. One of the two outputs of power divider 3 is connected to a first 90° bridge coupler 5, and the other is connected to a second 90° bridge coupler 4, so that the captured transient microwave signals are transmitted to dual-polarization dual-drive electro-optic modulator 2 through these two 90° bridge couplers respectively.

[0037] like Figure 2 As shown, the dual-polarization dual-drive electro-optic modulator 2 includes a first branch operating in the X-polarization state, a second branch operating in the Y-polarization state, and a polarization combiner 24 connected to the ends of the two branches. The first and second branches operate in orthogonal polarization states. A first dual-drive electro-optic modulator 21 (specifically a first dual-drive Mach-Zehnder modulator, DDMZM) operating in the X-polarization state is connected to the first branch. x The RF input terminal of the first dual-drive electro-optic modulator 21 is connected to the output terminal of the first 90° bridge coupler 5, and the output terminal of the first dual-drive electro-optic modulator 21 is connected to the X-polarized light input terminal of the polarization beam combiner 24 (PBC). A second dual-drive electro-optic modulator 22 (specifically a second dual-drive Mach-Zehnder modulator, DDMZM) operating in the Y-polarized state is connected in series in the second branch. y The second dual-drive electro-optic modulator 22 has its RF input connected to the output of the second 90° bridge coupler 4, and its output connected to the Y-polarized light input of the polarization combiner 24. The output of the polarization combiner 24 is connected to the input of the optical notch filter 6.

[0038] The input terminal of the first 90° bridge coupler 5 is connected to one output terminal of the power divider 3, and the two output terminals of the first 90° bridge coupler 5 are each connected to one RF input terminal of the first dual-drive electro-optic modulator 21. The first 90° bridge coupler 5 is used to load a transient microwave signal onto the optical carrier signal modulated by the first branch. The input terminal of the second 90° bridge coupler 4 is connected to the other output terminal of the power divider 3, and the two output terminals of the second 90° bridge coupler 4 are each connected to one RF input terminal of the second dual-drive electro-optic modulator 22. The second 90° bridge coupler 4 is used to adjust the transient microwave signal into an RF signal with a 90° phase difference before loading it onto the optical carrier signal modulated by the second branch.

[0039] The dual-polarization dual-drive electro-optic modulator 2 is used to load the radio frequency signals with a 90° phase difference from the output of two 90° bridge couplers onto the optical carrier signals modulated by the two branches respectively, so as to perform single-sideband modulation on the input optical carrier signals, thereby generating a positive first-order single-sideband modulation signal in the first branch and a negative first-order single-sideband modulation signal in the second branch.

[0040] The input of optical notch filter 6 is connected to the output of polarization combiner 24, and the output of optical notch filter 6 is connected to the input of polarization controller 7. Optical notch filter 6 is used to suppress the power of the optical carrier modulation signal loaded with radio frequency signal output from dual-polarization dual-drive electro-optic modulator 2, so that the positive first-order sideband and negative first-order sideband become the dominant frequency components of the single-sideband modulation signal. The input of polarization controller 7 is connected to the output of optical notch filter 6, and the output of polarization controller 7 is connected to erbium-doped fiber amplifier 8. Polarization controller 7 is used to adjust the polarization state of the optical carrier modulation signal output from optical notch filter 6, so that it is consistent with the polarization state of the optical carrier modulation signal output from dual-polarization dual-drive electro-optic modulator 2. The input of erbium-doped fiber amplifier 8 is connected to the output of polarization controller 7, and the output of erbium-doped fiber amplifier 8 is connected to polarization beamsplitter 9. Erbium-doped fiber amplifier 8 is used to amplify the power of the optical carrier modulation signal output from polarization controller 7. The input of polarization beamsplitter 9 is connected to the output of erbium-doped fiber amplifier 8. The X-polarized light output of polarization beamsplitter 9 is connected to the first instantaneous optical frequency measurement module 10, and the Y-polarized light output of polarization beamsplitter 9 is connected to the second instantaneous optical frequency measurement module 11. Polarization beamsplitter 9 is used to orthogonally separate the optical carrier modulation signal output from erbium-doped fiber amplifier 8 into X-polarized and Y-polarized states. It outputs an upper sideband modulated optical carrier modulation signal to the first instantaneous optical frequency measurement module 10 through the X-polarized light output and a lower sideband modulated optical carrier modulation signal to the second instantaneous optical frequency measurement module 11 through the Y-polarized light output.

[0041] Figure 1In this system, the input of the first instantaneous optical frequency measurement module 10 is connected to the X-polarized light output of the polarization beam splitter 9, and the output of the first instantaneous optical frequency measurement module 10 is connected to the signal processing system 12. The first instantaneous optical frequency measurement module 10 is used to measure the instantaneous frequency of the positive first-order single-sideband modulation signal of the upper sideband modulated optical carrier modulation signal. The input of the second instantaneous optical frequency measurement module 11 is connected to the Y-polarized light output of the polarization beam splitter 9, and the output of the second instantaneous optical frequency measurement module 11 is connected to the signal processing system 12. The second instantaneous optical frequency measurement module 11 is used to measure the instantaneous frequency of the negative first-order single-sideband modulation signal of the lower sideband modulated optical carrier modulation signal. The signal processing system 12 is connected to the first instantaneous optical frequency measurement module 10 and the second instantaneous optical frequency measurement module 11, respectively, and is used to receive the measurement results of the positive first-order single-sideband modulation signal by the first instantaneous optical frequency measurement module 10 and the measurement results of the negative first-order single-sideband modulation signal by the second instantaneous optical frequency measurement module 11, thereby calculating the frequency of the instantaneous microwave signal captured by the detection radar.

[0042] like Figure 2 As shown, a specific implementation of the first instantaneous light frequency measurement module 10 and the second instantaneous light frequency measurement module 11 is as follows: The first instantaneous optical frequency measurement module 10 includes a first optical circulator 10-1, a first 3×3 coupler module 10-2, a first photodetector 10-3, a second photodetector 10-4, and a third photodetector 10-5. The input terminal of the first optical circulator 10-1 is connected to the X-polarized light output terminal of the polarization beam splitter 9. The input / output terminal of the first optical circulator 10-1 is connected to the first 3×3 coupler module 10-2, and the output terminal of the first optical circulator 10-1 is connected to the input terminal of the first photodetector 10-3. The first optical circulator 10-1 is used to transmit the upper sideband modulated optical carrier modulation signal to the first 3×3 coupler module 10-2 and output the optical signal fed back from the first 3×3 coupler module 10-2 to the first photodetector 10-3. The input / output terminals of the first 3×3 coupler module 10-2 are connected to the input / output terminals of the first optical circulator 10-1. The first output terminal of the first 3×3 coupler module 10-2 is connected to the input terminal of the second photodetector 10-4, and the second output terminal of the first 3×3 coupler module 10-2 is connected to the input terminal of the third photodetector 10-5. The first 3×3 coupler module 10-2 is used to map the upper sideband modulated optical carrier modulation signal into an optical signal carrying corresponding phase information. The input terminal of the first photodetector 10-3 is connected to the output terminal of the first optical circulator 10-1, and the output terminal of the first photodetector 10-3 is connected to the signal processing system 12. The first photodetector 10-3 is used to convert the optical signal carrying corresponding phase information into an electrical signal that can be processed by the signal processing system 12. The input terminal of the second photodetector 10-4 is connected to the first output terminal of the first 3×3 coupler module 10-2, and the output terminal of the second photodetector 10-4 is connected to the signal processing system 12, used to convert the optical signal carrying corresponding phase information into an electrical signal that can be processed by the signal processing system. The input terminal of the third photodetector 10-5 is connected to the second output terminal of the first 3×3 coupler module 10-2, and the output terminal of the third photodetector 10-5 is connected to the signal processing system 12. The third photodetector 10-5 is used to convert the optical signal carrying the corresponding phase information into an electrical signal that can be processed by the signal processing system.

[0043] The second instantaneous optical frequency measurement module 11 includes a second optical circulator 11-1, a second 3×3 coupler module 11-2, a fifth photodetector 11-3, a sixth photodetector 11-4, and a seventh photodetector 11-5. The input terminal of the second optical circulator 11-1 is connected to the Y-polarized light output terminal of the polarization beam splitter 9. The input / output terminals of the second optical circulator 11-1 are connected to the input / output terminals of the second 3×3 coupler module 11-2, and the output terminal of the second optical circulator 11-1 is connected to the input terminal of the fifth photodetector 11-3. The second optical circulator 11-1 is used to transmit the lower sideband modulated optical carrier modulation signal to the second 3×3 coupler module 11-2 and output the optical signal fed back from the second 3×3 coupler module 11-2 to the fifth photodetector 11-3. The input / output terminals of the second 3×3 coupler module 11-2 are connected to the input / output terminals of the second optical circulator 11-1. The first output terminal of the second 3×3 coupler module 11-2 is connected to the input terminal of the sixth photodetector 11-4, and the second output terminal of the second 3×3 coupler module 11-2 is connected to the input terminal of the seventh photodetector 11-5. The second 3×3 coupler module 11-2 is used to map the lower sideband modulated optical carrier modulation signal into an optical signal carrying corresponding phase information. The input terminal of the fifth photodetector 11-3 is connected to the output terminal of the second optical circulator 11-1, and the output terminal of the fifth photodetector 11-3 is connected to the signal processing system 12. The fifth photodetector 11-3 is used to convert the optical signal carrying corresponding phase information into an electrical signal that can be processed by the signal processing system. The input terminal of the sixth photodetector 11-4 is connected to the first output terminal of the second 3×3 coupler module 11-2, and the output terminal of the sixth photodetector 11-4 is connected to the signal processing system 12. The sixth photodetector 11-4 converts the optical signal carrying corresponding phase information into an electrical signal that can be processed by the signal processing system. The input terminal of the seventh photodetector 11-5 is connected to the second output terminal of the second 3×3 coupler module 11-2, and the output terminal of the seventh photodetector 11-5 is connected to the signal processing system 12. The seventh photodetector 11-5 converts the optical signal carrying corresponding phase information into an electrical signal that can be processed by the signal processing system.

[0044] The instantaneous microwave frequency measurement system of this invention operates as follows: Laser 1 transmits an optical carrier signal to dual-polarization dual-drive electro-optic modulator 2 via optical fiber. The first dual-drive electro-optic modulator 21 and the second dual-drive electro-optic modulator 22 inside the dual-polarization dual-drive electro-optic modulator 2 modulate the input optical carrier signal respectively. The bias controller sets the operating point of the dual-drive electro-optic modulator to an orthogonal operating point. Power divider 3 splits the input RF signal into two signals of equal power, which are input to two 90° bridge couplers 4 and 5. The two RF signals output from the two 90° bridge couplers, with a 90° phase difference, are loaded onto the modulated optical carrier signal, generating a positive first-order single-sideband modulated signal in the first branch and a negative first-order single-sideband modulated signal in the second branch. The optical carrier signal loaded with the RF signal is input to optical notch filter 6, which suppresses the power of the optical carrier, thereby making the power of the positive and negative first-order sidebands of the first and second branch modulated signals greater than the power of other sidebands, thus making the positive and negative first-order sidebands the dominant frequency components of the single-sideband modulated signal. The polarization controller 7 adjusts the polarization state of the optical signal suppressed by the optical notch filter 6 to match the polarization state of the modulation signal emitted by the dual-polarization dual-drive electro-optic modulator 2 before outputting it. The erbium-doped fiber amplifier 8 amplifies the optical signal output by the polarization controller 7 and then inputs it into the polarization beam splitter 9, which separates the single-sideband modulation signals of the first and second branches. The single-sideband modulation signal of the first branch enters the first optical circulator 10-1 of the first instantaneous optical frequency measurement module 10. The optical signal at the input / output end of the first optical circulator 10-1 enters the first 3×3 coupler module 10-2. The first 3×3 coupler module 10-2 maps the single-sideband modulation signal into an optical signal carrying corresponding phase information and inputs it into the second photodetector 10-4 and the third photodetector 10-5. The first optical circulator 10-1 receives the optical signal returned from the first 3×3 coupler module 10-2 and outputs it to the first photodetector 10-3. The second branch follows the same procedure. The signal processing system 12 processes the signals output by the first photodetector 10-3, the second photodetector 10-4, the third photodetector 10-5, the fifth photodetector 11-3, the sixth photodetector 11-4, and the seventh photodetector 11-5 to obtain the frequency of the instantaneous microwave signal captured by the detection radar. Example 2

[0045] like Figure 3 As shown, the system configuration of this embodiment is basically the same as that of embodiment 1, except that the specific implementation of the first instantaneous light frequency measurement module 10 and the second instantaneous light frequency measurement module 11 is different.

[0046] The first instantaneous optical frequency measurement module 10 includes a first polarization beam shifter 10-6, a first 90° polarization rotator 10-7, a first polarizer 10-8, a first optical differential delay element 10-9, a first lens 10-10, a first unpolarization beam splitter 10-11, a first Wollaston prism 10-12, a first quarter-wave plate 10-13, a second Wollaston prism 10-14, a first photodetector 10-3, a second photodetector 10-4, a third photodetector 10-5, and a fourth photodetector 10-15. The second instantaneous optical frequency measurement module 11 includes a second polarization beam shifter 11-6, a second 90° polarization rotator 11-7, a second polarizer 11-8, a second optical differential delay element 11-9, a second lens 11-10, a second unpolarized beam splitter 11-11, a third Wollaston prism 11-12, a second quarter-wave plate 11-13, a fourth Wollaston prism 11-14, a fifth photodetector 11-3, a sixth photodetector 11-4, a seventh photodetector 11-5, and an eighth photodetector 11-15.

[0047] The upper-sideband modulated optical carrier signal, separated by polarization beam splitter 9, enters the first polarization beam shifter 10-6, shifting the first and second beams with orthogonal polarization components. Then, a first 90° polarization rotator 10-7 is placed within one of the beams, ensuring both beams have the same polarization state. A first polarizer 10-8 eliminates polarization errors caused by defects in the first 90° polarization rotator 10-7, ensuring both beams have the same polarization state. A first optical differential delay element 10-9 creates an optical delay between the two beams, and a first lens 10-10 focuses the two beams. A first unpolarized beam splitter 10-11 receives the light from the first optical differential delay element 10-9 and splits it into two mutually perpendicular beams. A first Wollaston prism 10-12 splits one beam, generating two beams with orthogonal polarization components. These two beams then enter the first photodetector 10-3 and the second photodetector 10-4. The first quarter-wave plate 10-13 introduces another beam of light with a π / 2 phase delay, which is then split into two beams with orthogonal polarization components by the second Wollaston prism 10-14. These two beams of light enter the third photodetector 10-5 and the fourth photodetector 10-15. The first photodetector 10-3 to the fourth photodetector 10-15 convert the input light signals into electrical signals, which are then sent to the signal processing system for calculation. The second branch follows the same procedure. The signal processing system 12 processes the signals output from the eight photodetectors to obtain the frequency of the instantaneous microwave signal captured by the radar.

[0048] exist Figure 4In the two spectra shown in (a) and (b), the dashed line represents the amplitude response of the optical notch filter. It can be seen that the optical notch filter suppresses the optical carrier. By setting the operating points of the two dual-drive Mach-Zehnder modulators as orthogonal operating points, and under the action of two 90° bridge couplers, respectively... Figure 4 The first branch positive first-order single-sideband modulation shown in (c) and Figure 4 The second branch, shown in (d), is a negative first-order single-sideband modulation. The carrier signal is suppressed by an optical notch filter, making the positive and negative first-order sidebands the dominant frequency components. This significantly reduces the influence of other sidebands on the measured signal.

[0049] exist Figure 5 In the diagram, the solid line represents the frequency value measured by the instantaneous photofrequency measurement module of the first branch, and the dashed line represents the frequency value measured by the instantaneous photofrequency measurement module of the second branch. When the laser experiences frequency jitter, the measured frequency jitter of the first and second branches is almost identical. After subtracting the two values, the frequency jitter of the first and second branches cancels each other out, thus significantly reducing the frequency jitter.

Claims

1. An instantaneous microwave frequency measurement system, characterized in that, It includes a laser, a dual-polarization dual-drive electro-optic modulator, an optical trap, a polarization controller, an erbium-doped fiber amplifier, and a polarization beam splitter connected in sequence. The two outputs of the polarization beam splitter are connected to the signal processing system after passing through an instantaneous optical frequency measurement module. It also includes an electrical power divider, whose input is used to connect to a detection radar that captures transient microwave signals from the outside world, and whose two outputs are respectively connected to a first 90° bridge coupler and a second 90° bridge coupler. The dual-polarization dual-drive electro-optic modulator includes a first branch operating in the X-polarization state, a second branch operating in the Y-polarization state, and a polarization combiner connected to the ends of the two branches; a first dual-drive electro-optic modulator is provided on the first branch, and a second dual-drive electro-optic modulator is provided on the second branch. The radio frequency input terminals of the two dual-drive electro-optic modulators are respectively connected to the output terminals of the two 90° bridge couplers; the dual-polarization dual-drive electro-optic modulator is used to load the radio frequency signals with a 90° phase difference output from the two 90° bridge couplers onto the optical carrier signals modulated by the two branches respectively, so as to perform single-sideband modulation on the input optical carrier signals, thereby generating positive first-order and negative first-order single-sideband modulation signals in the two branches respectively; The optical notch filter is used to suppress the power of the optical carrier modulation signal loaded with radio frequency signal output from the dual-polarization dual-drive electro-optic modulator, so that the positive first-order sideband and negative first-order sideband become the main frequency components of the single-sideband modulation signal; the polarization controller is used to adjust the polarization state of the optical carrier modulation signal output from the optical notch filter, so that it is consistent with the polarization state of the optical carrier modulation signal output from the dual-polarization dual-drive electro-optic modulator; the erbium-doped fiber amplifier is used to amplify the power of the optical carrier modulation signal output from the polarization controller; the polarization beam splitter is used to orthogonally separate the X-polarization state and Y-polarization state of the optical carrier modulation signal output from the erbium-doped fiber amplifier, and output the upper sideband modulated optical carrier modulation signal and the lower sideband modulated optical carrier modulation signal through two output terminals respectively; Two instantaneous optical frequency measurement modules are used to measure the instantaneous frequency of the positive first-order single-sideband modulation signal of the upper sideband modulated optical carrier modulation signal and the instantaneous frequency of the negative first-order single-sideband modulation signal of the lower sideband modulated optical carrier modulation signal, respectively. The signal processing system is used to receive the measurement results of the positive and negative first-order single-sideband modulation signals by the two instantaneous optical frequency measurement modules, and to calculate the frequency of the instantaneous microwave signal captured by the detection radar.

2. The instantaneous microwave frequency measurement system according to claim 1, characterized in that, The first branch of the dual-polarization dual-drive electro-optic modulator is connected to a first dual-drive electro-optic modulator operating in the X-polarization state. The second branch is connected in series with a second dual-drive electro-optic modulator operating in the Y-polarization state and a third 90° polarization rotator. The two branches operate in orthogonal polarization states. The end of the first branch is connected to the X-polarization state light input terminal of the polarization beam combiner, and the end of the second branch is connected to the Y-polarization state light input terminal of the polarization beam combiner.

3. The instantaneous microwave frequency measurement system according to claim 1, characterized in that, The two instantaneous light frequency measurement modules are the first instantaneous light frequency measurement module and the second instantaneous light frequency measurement module, respectively. The first instantaneous light frequency measurement module includes: The first optical circulator has an input terminal connected to a polarization beam splitter, an input / output terminal connected to a first 3×3 coupler module, and an output terminal connected to a first photodetector. It is used to transmit the upper sideband modulated optical carrier modulation signal to the first 3×3 coupler module and output the optical signal fed back by the first 3×3 coupler module to the first photodetector. The first 3×3 coupler module has its input / output terminals connected to the input / output terminals of the first optical circulator, its first output terminal connected to the second photodetector, and its second output terminal connected to the third photodetector. It is used to map the upper sideband modulated optical carrier modulation signal into an optical signal carrying corresponding phase information. The first photodetector has its input end connected to the first optical circulator and its output end connected to the signal processing system, and is used to convert the optical signal carrying the corresponding phase information into an electrical signal that can be processed by the signal processing system. The second photodetector, whose input is connected to the first 3×3 coupler module and whose output is connected to the signal processing system, is used to convert the optical signal carrying corresponding phase information into an electrical signal that can be processed by the signal processing system; and The third photodetector has its input end connected to the first 3×3 coupler module and its output end connected to the signal processing system. It is used to convert the optical signal carrying the corresponding phase information into an electrical signal that can be processed by the signal processing system.

4. The instantaneous microwave frequency measurement system according to claim 3, characterized in that, The structure of the second instantaneous light frequency measurement module is the same as that of the first instantaneous light frequency measurement module.

5. The instantaneous microwave frequency measurement system according to claim 1, characterized in that, The two instantaneous light frequency measurement modules are the first instantaneous light frequency measurement module and the second instantaneous light frequency measurement module, respectively. The first instantaneous optical frequency measurement module includes a first polarized beam shifter, a first 90° polarization rotator, a first polarizer, a first optical differential delay element, a first lens, and a first unpolarized beam splitter connected in sequence. The first polarized beam shifter is used to shift the first beam and the second beam, which have orthogonal polarization components. The first 90° polarization rotator and the first polarizer are used to make the two beams have the same polarization state. The first optical differential delay element is used to generate an optical delay between the two beams. The first unpolarized beam splitter separates the received light into two mutually perpendicular beams. One output of the first unpolarized beam splitter is connected to the first Wollaston prism, and its other output is connected to the second Wollaston prism after passing through the first quarter-wave plate. Both Wollaston prisms are used to split a single beam of light, generating two beams with orthogonal polarization components. The two outputs of the first Wollaston prism are connected to the first photodetector and the second photodetector, respectively, and the two outputs of the second Wollaston prism are connected to the third photodetector and the fourth photodetector, respectively. All four photodetectors are connected to the signal processing system.

6. The instantaneous microwave frequency measurement system according to claim 5, characterized in that, The structure of the second instantaneous light frequency measurement module is the same as that of the first instantaneous light frequency measurement module.

7. A method for instantaneous microwave frequency measurement, characterized in that, Includes the following steps: S1. A transient microwave frequency measurement system as described in any one of claims 1-6 is provided; the two transient microwave frequency measurement modules are a first transient microwave frequency measurement module and a second transient microwave frequency measurement module, respectively; S2. The laser transmits an optical carrier signal to the dual-polarization dual-drive electro-optic modulator. The power divider transmits the external radio frequency signal from the detection radar to the dual-polarization dual-drive electro-optic modulator through two 90° bridge couplers. The first 90° bridge coupler loads the captured external radio frequency signal onto the optical carrier signal modulated by the first branch for upper sideband modulation. The second 90° bridge coupler adjusts the captured external radio frequency signal to a radio frequency signal with a 90° phase difference and loads it onto the optical carrier signal modulated by the second branch for lower sideband modulation. The dual-polarization dual-drive electro-optic modulator generates a positive first-order single-sideband modulation signal in the first branch and a negative first-order single-sideband modulation signal in the second branch through single-side modulation of the two branches. S3. The optical notch filter suppresses the power of the optical carrier modulation signal loaded with radio frequency signal output from the dual polarization dual drive electro-optic modulator so that the positive first-order sideband and the negative first-order sideband become the main frequency components of the single-sideband modulation signal. S4. The polarization controller adjusts the polarization state of the optical carrier modulation signal output by the optical notch filter to make it consistent with the polarization state of the optical carrier modulation signal output by the dual-polarization dual-drive electro-optic modulator. S5. The erbium-doped fiber amplifier amplifies the optical signal output from the polarization controller. The polarization beam splitter orthogonally separates the optical carrier modulation signal output from the erbium-doped fiber amplifier into X-polarization and Y-polarization states, obtaining an upper sideband modulated optical carrier modulation signal and a lower sideband modulated optical carrier modulation signal. The upper sideband modulated optical carrier modulation signal is output to the first instantaneous optical frequency measurement module through the X-polarization state optical output terminal, and the lower sideband modulated optical carrier modulation signal is output to the second instantaneous optical frequency measurement module through the Y-polarization state optical output terminal. S6. The first instantaneous optical frequency measurement module measures the instantaneous frequency of the positive first-order single-sideband of the upper sideband modulated optical carrier modulation signal and inputs the measurement result into the signal processing system; the second instantaneous optical frequency measurement module measures the instantaneous frequency of the negative first-order single-sideband of the lower sideband modulated optical carrier modulation signal and inputs the measurement result into the signal processing system. S7. The signal processing system calculates and processes the received measurement results to obtain the frequency of the instantaneous microwave signal captured by the detection radar.

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