Microwave frequency measuring device based on frequency modulation light source and time delay phase discrimination

Abstract

The invention discloses a microwave frequency measuring device based on a frequency modulation light source and time delay phase discrimination, and belongs to the field of microwave photon signal detection. The method comprises the following steps: firstly, measuring a signal in a large frequency range through the frequency-time mapping characteristic of a frequency modulation light source frequency measurement system, and carrying out secondary measurement on an intermediate frequency signal carrying to-be-measured frequency information in a time delay phase discrimination frequency measurement system through frequency-phase-voltage mapping through frequency conversion processing according to a measurement result; the precision of the second measurement is greatly improved based on the first measurement, intermediate frequency signals are generated by setting local oscillation signals with different frequencies, the time delay phase discrimination frequency measurement system can process any frequency signal measured by the frequency modulation light source frequency measurement system, measurement errors in the measurement range of the time delay phase discrimination frequency measurement system are emphatically researched, and the measurement accuracy of the time delay phase discrimination frequency measurement system is improved. Therefore, the degree of measurement precision optimization can be evaluated. According to the device, the characteristics of large bandwidth and high precision of frequency measurement are guaranteed at the same time, and microwave frequency measurement with excellent performance can be realized.

Description

Technical Field

[0001] This invention belongs to the field of microwave photonic signal detection, specifically relating to a microwave frequency measurement device based on a frequency-modulated light source and time-delay phase detection. Background Technology

[0002] As radar and electronic reconnaissance systems place higher demands on the generation, transmission, control, and processing of microwave signals, traditional electronic technologies have significant room for improvement in detecting high-bandwidth signals. Against this backdrop, signal frequency measurement based on microwave photonics is receiving attention and research. Its core idea is to convert frequencies into other parameters that are easier to identify and detect. The main technical routes include frequency-to-space mapping (FTSM), which uses optical frequency combs, wavelength division multiplexers, and array photodetectors to construct channelized systems (WY Xu, D. Zhu, and SL Pan. Opt. Eng., 55(4): 046106, 2016). This method requires large-scale array devices and has high system complexity. Frequency-to-phase-slope mapping (FTPSM), which uses components such as phase modulators and tunable optical delay lines to construct microwave phase detectors (JZShi, FZ Zhang, D. Ben, and SL Pan. IEEE Trans. Microw. Theory Techn., 67(2): 544-551, 2019), is an example of such a method. However, this method is affected by factors such as I / Q demodulation phase mismatch. Frequency-to-power mapping (FTPM), which uses components such as electrical delay lines and polarization multiplexing modulators to construct amplitude comparison functions (Li, L. Pei, T. Ning, J. Zheng, Y. Li, and R.He. J. Lightw. Technol., 38(8): 2285–2291, 2020), is an example of a method that can achieve instantaneous frequency measurement and is currently the mainstream method for microwave photonic frequency measurement. Frequency-to-time mapping (FTTM), which uses a linear frequency modulation source to establish the relationship between the frequency to be measured and time (X. Li, Z. Fan, J. Su, Y. Wang, S. Shi, and Q. Qiu. Opt. Exp., 32(10): 18127-18138, 2024), is an efficient solution for the identification and measurement of complex multi-frequency signals. Currently, the measurement of microwave signals faces the problem of mutual constraints between measurement accuracy and measurement range. Therefore, achieving large-scale, high-precision microwave photon frequency measurement is a key focus of current research and improvement. Summary of the Invention

[0003] The purpose of this invention is to address the problems existing in the prior art by proposing a microwave frequency measurement device based on a frequency-modulated light source and time-delay phase detection. This microwave frequency measurement device can solve the problem of the mutual constraint between measurement accuracy and measurement range, and can achieve high-precision measurement of microwave signals over a wide frequency range.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A microwave frequency measurement device based on frequency-modulated light source and time-delay phase detection includes a linear frequency-modulated laser, a first electro-optic modulator, a 2×1 fiber coupler, a photodetector, a first bandpass filter, a first analog-to-digital converter module, a first signal generator, a second signal generator, an RF power divider, an RF mixer, a second bandpass filter, a continuous wave laser, a first 1×2 fiber coupler, a second electro-optic modulator, a second 1×2 fiber coupler, a tunable optical delay line, a dual-channel photodetector, a phase detection module, a second analog-to-digital converter module, and a feedback control module.

[0006] The linear frequency modulated laser is connected to end I of a 2×1 fiber coupler. The first signal generator is connected to an RF power divider. End III of the RF power divider is connected to the RF port of the first electro-optic modulator. The optical output port of the first electro-optic modulator is connected to end II of the 2×1 fiber coupler. The output of the 2×1 fiber coupler is connected to the input of a photodetector. The output of the photodetector is connected to the input of a first bandpass filter. The output of the first bandpass filter is connected to the first analog-to-digital converter module. End IV of the RF power divider is connected to one input port of an RF mixer. The second signal generator is connected to the other input port of the RF mixer. The output of the RF mixer is connected to the input of the second bandpass filter. The continuous wave laser is connected to the input of the first 1×2 fiber coupler. The first 1×2 fiber coupler V is connected to the optical input port of the first electro-optic modulator, the first 1×2 fiber coupler VI is connected to the optical input port of the second electro-optic modulator, the output of the second bandpass filter is connected to the radio frequency port of the second electro-optic modulator, the optical output port of the second electro-optic modulator is connected to the input of the second 1×2 fiber coupler, the second 1×2 fiber coupler VII is connected to the tunable optical delay line, the tunable optical delay line is connected to one optical input port of the dual-channel photodetector, the second 1×2 fiber coupler VIII is connected to the other optical input port of the dual-channel photodetector, the two output ports of the dual-channel photodetector are connected to the phase detection module, and the output of the phase detection module is connected to the second analog-to-digital converter module.

[0007] The analysis results of the first analog-to-digital conversion module are sent to the feedback control module, which controls the signal frequency of the local oscillator output of the second signal generator. The analysis results of the second analog-to-digital conversion module are used as the final output.

[0008] The microwave frequency measuring device provided by this invention includes a frequency modulation light source frequency measuring system and a time delay phase detection frequency measuring system. The process of realizing microwave frequency measurement is as follows:

[0009] A linear frequency-modulated laser outputs frequency-modulated continuous light with linear frequency-time characteristics. The output of the continuous wave laser is fed into a first electro-optic modulator via a first 1×2 fiber coupler. The signal to be measured generated by a first signal generator is input to the RF port of the first electro-optic modulator after passing through an RF power divider. The bias voltage of the first electro-optic modulator is adjusted to make it operate at the quadrature transmission point (QTP) to generate double-sideband (DSB) modulation. At this time, the light field output from the first electro-optic modulator can be expressed as:

[0010] (1)

[0011] In the formula, m = πV RF / V π V represents the modulation coefficient. RF and f e V represents the initial amplitude and frequency of the microwave signal under test, respectively. π The half-wave voltages E0 and f of the electro-optic modulator are represented by these two values. c Let J0 and J1 represent the initial amplitude and frequency of the optical carrier wave, respectively, and let t be the time. It is the symbol for imaginary numbers.

[0012] Set the frequency sweep range of the linear frequency modulated laser to cover the carrier wave f of the output optical field of the first electro-optic modulator. c With the lower band f c -f e When the instantaneous frequency of the linearly frequency-modulated laser is different from the lower sideband f c -f e and carrier f c The beat frequency is equal to the center frequency f of the first bandpass filter. BPF At that time, the instantaneous frequency of the linearly frequency-modulated laser will be equal to f c -f e -f BPF f c -f e +f BPF f c -f BPF f c +f BPFFour pulses are generated at the corresponding time points and reflected in the first analog-to-digital converter module. The first analog-to-digital converter module calculates the interval between the time corresponding to the center points of the first two pulses and the time corresponding to the center points of the last two pulses, denoted as Δt. Then, the frequency measurement value f of the signal to be measured generated by the first signal generator is obtained. e ʹ It can be represented as:

[0013] (2)

[0014] In the formula, γ represents the sweep rate of the linear frequency modulated laser, and Δt represents the interval between the time corresponding to the center points of the first two pulses and the time corresponding to the center points of the last two pulses.

[0015] Then, the result f of the frequency measurement system of the frequency-modulated light source output by the first analog-to-digital conversion module is used. e ʹ As a guide, the feedback control module is used to control the local oscillator signal output frequency of the second signal generator. At this time, the frequency of the local oscillator signal output is:

[0016] (3)

[0017] In the formula f IF The preset ideal intermediate frequency remains at a certain value in multiple measurements. However, due to the frequency modulation light source measurement system, the measured value f... e ʹ With the true value f e There is a discrepancy, therefore the actual intermediate frequency after passing through the RF mixer and the second bandpass filter is:

[0018] (4)

[0019] In the formula f IF ʹ This is the actual intermediate frequency signal frequency.

[0020] When the intermediate frequency signal is fed into the second electro-optic modulator, it modulates the carrier wave from the first 1×2 fiber coupler. The output light wave is then split into two paths after passing through the second 1×2 fiber coupler. One path is directly fed to one port of the dual-channel photodetector, and the other path is fed into the other port of the dual-channel photodetector after passing through an adjustable optical delay line. The two electrical signals output from the dual-channel photodetector enter the input terminal of the phase detection module, which identifies the phase difference between the two signals introduced by the adjustable optical delay line and forms a DC voltage output presented to the second analog-to-digital conversion module. Since the phase difference is proportional to the frequency of the intermediate frequency signal, this process realizes frequency-phase-voltage mapping, which can be expressed by the following formula:

[0021] (5)

[0022] In the formula, k and c are the working parameters of the phase detection module itself; Δφ is the phase difference between the two signals entering the phase detection module, and its variation range does not exceed 360°; τ is the time delay between these two signals; i is related to the phase discrimination period of the phase detection module, and its value is 1, 2, …. Within a single phase discrimination period, when τ is determined, the unambiguous frequency range that the system can identify is 1 / τ. At this time, a specific frequency will correspond to a specific voltage output, and the true intermediate frequency f can be calculated according to the voltage value of the second analog-to-digital conversion module. IF ʹ , at this time, the frequency measurement value f of the time-delay phase discrimination frequency measurement system e ʹʹ can be expressed as:

[0023] (6)

[0024] In the formula, p = i - 1, which is a value related to the phase discrimination period of the phase detection module. The time-delay phase discrimination frequency measurement system has higher accuracy than the frequency-modulated light source frequency measurement system. That is, the measurement error of the time-delay phase discrimination frequency measurement system is less than that of the frequency-modulated light source frequency measurement system, which is expressed as formula (7):

[0025] (7)

[0026] To make the above process work properly, the measurement error of the frequency-modulated light source frequency measurement system must be less than the measurement range R of the time-delay phase discrimination frequency measurement system, that is, |f e ʹ - f e | < R. The error between the result f e ʹ of the frequency-modulated light source frequency measurement system and the true value f e will be eliminated within the measurement range R of the time-delay phase discrimination frequency measurement system, thereby achieving a substantial optimization of the measurement accuracy.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] This invention combines a frequency-modulated light source measurement system and a time-delay phase-detection frequency measurement system for signal frequency measurement. First, the frequency-time mapping characteristic of the frequency-modulated light source measurement system is used to measure signals over a wide frequency range. Based on the measurement results, the intermediate frequency (IF) signal carrying the frequency information to be measured is converted through frequency conversion and then measured a second time in the time-delay phase-detection frequency measurement system using frequency-phase-voltage mapping. The second measurement significantly improves accuracy compared to the first. By setting local oscillator signals of different frequencies to generate IF signals, the time-delay phase-detection frequency measurement system can process any frequency signal measured by the frequency-modulated light source measurement system. By focusing on the measurement error within the measurement range of the time-delay phase-detection frequency measurement system, the degree of optimization in measurement accuracy can be evaluated. This device simultaneously ensures a large bandwidth and high precision in frequency measurement, enabling high-performance microwave frequency measurement. Attached Figure Description

[0029] Figure 1 A schematic diagram of a microwave frequency measurement device based on a frequency-modulated light source and time delay phase detection provided by the present invention;

[0030] Figure 2 The error is based on the measured frequency modulation light source frequency measurement system, with a frequency measurement range covering 2-40 GHz;

[0031] Figure 3 The theoretical voltage-phase difference curve for the phase detection module used;

[0032] Figure 4 This represents the error of the measured time delay phase detection and frequency measurement system. Detailed Implementation

[0033] The apparatus and implementation methods of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0034] Example

[0035] Figure 1This is a schematic diagram of a microwave frequency measurement device based on a frequency-modulated light source and a time-delay phase detection provided by the present invention. The device mainly includes a frequency-modulated light source frequency measurement system and a time-delay phase detection frequency measurement system, which are connected by an intermediate frequency converter. The feedback control module controls the signal frequency of the second signal generator to output local oscillator signals of different frequencies. The optical and electrical signals in the entire microwave photonic link structure path are marked. Specifically, the microwave frequency measurement device based on frequency-modulated light source and time-delay phase detection includes a linear frequency-modulated laser 1, a first electro-optic modulator 2, a 2×1 fiber coupler 3, a photodetector 4, a first bandpass filter 5, a first analog-to-digital converter 6, a first signal generator 7, a second signal generator 8, an RF power divider 9, an RF mixer 10, a second bandpass filter 11, a continuous wave laser 12, a first 1×2 fiber coupler 13, a second electro-optic modulator 14, a second 1×2 fiber coupler 15, a tunable optical delay line 16, a dual-channel photodetector 17, a phase detection module 18, a second analog-to-digital converter 19, and a feedback control module 20.

[0036] The linear frequency modulated laser 1 is connected to end I of the 2×1 fiber coupler 3. The first signal generator 7 is connected to the RF power divider 9. End III of the RF power divider 9 is connected to the RF port of the first electro-optic modulator 2. The optical output port of the first electro-optic modulator 2 is connected to end II of the 2×1 fiber coupler 3. The output of the 2×1 fiber coupler 3 is connected to the input of the photodetector 4. The output of the photodetector 4 is connected to the input of the first bandpass filter 5. The output of the first bandpass filter 5 is connected to the first analog-to-digital converter 6. End IV of the RF power divider 9 is connected to one input port of the RF mixer 10. The second signal generator 8 is connected to the other input port of the RF mixer 10. The output of the RF mixer 10 is connected to the input of the second bandpass filter 11. The continuous wave laser 12 is connected to the input of the first 1×2 fiber coupler. End V of the first 1×2 fiber coupler is connected to the optical input port of the first electro-optic modulator 2. The VI end of the fiber coupler is connected to the optical input port of the second electro-optic modulator 14, the output end of the second bandpass filter 11 is connected to the RF port of the second electro-optic modulator 14, the optical output port of the second electro-optic modulator 14 is connected to the input end of the second 1×2 fiber coupler 15, the VII end of the second 1×2 fiber coupler 15 is connected to the tunable optical delay line 16, the tunable optical delay line 16 is connected to one optical input port of the dual-channel photodetector 17, the VIII end of the second 1×2 fiber coupler 15 is connected to the other optical input port of the dual-channel photodetector 17, the two output ports of the dual-channel photodetector 17 are connected to the phase detection module 18, the output end of the phase detection module 18 is connected to the second analog-to-digital converter module 19, the analysis result of the first analog-to-digital converter module 6 is sent to the feedback control module 20, the feedback control module 20 controls the signal frequency of the local oscillator output of the second signal generator 8, and the analysis result of the second analog-to-digital converter module 19 is used as the final output.

[0037] The microwave frequency measuring device provided by this invention includes a frequency modulation light source frequency measuring system and a time delay phase detection frequency measuring system. The process of realizing microwave frequency measurement is as follows:

[0038] The wavelength of the continuous wave laser 12 is set to 1550.00 nm, the frequency modulation rate of the linear frequency modulated laser 1 is 1.132 GHz / μs, the first electro-optic modulator 2 is set to DSB operation, and the first signal generator 7 generates 20 test signals in 2 GHz increments within the range of 2-40 GHz. For each frequency of the test signal, the sweeping light range of the linear frequency modulated laser can cover the optical sideband and optical carrier generated by the signal modulation. After the modulated optical signal and the continuous light wave interfere in the 2×1 fiber coupler 3, they enter the photodetector 4 for beat frequency. When the beat frequency of the optical sideband and the instantaneous frequency of the linear frequency modulated laser is equal to the center frequency of the first bandpass filter 5, a pair of pulses will be generated near a specific time point and presented on the first analog-to-digital conversion module 6. Similarly, the beat frequency of the optical carrier and the instantaneous frequency of the linear frequency modulated laser will also generate another pair of pulses. By reading the time interval between these two pairs of pulses, the measured value of the frequency of the test signal can be obtained according to the calculation method of formula (2). Frequency measurement results of the signal under test in the GHz range are as follows Figure 2 As shown, the measurement error of the frequency modulation light source measurement system is controlled within ±40 MHz.

[0039] Figure 3 The voltage-phase difference theoretical characteristics of the phase detection module used in this embodiment are shown. It has two monotonic voltage output curves in the phase detection range of -180° to 180°, and it exhibits symmetrical characteristics about the voltage axis. The center frequency of the second bandpass filter 11 used is 2.4 GHz.

[0040] In equation (5), the output voltage of the phase detection module is related to the intermediate frequency, and k and c are ±0.01 and 1.8 respectively. Therefore, equation (5) can be rewritten as:

[0041] (8)

[0042] To ensure the normal operation of the time delay phase detection and frequency measurement system, combined with, for example Figure 3 The theoretical voltage-phase difference curve and formula (8) of the phase detection module shown require that the time delay of the two electrical signals input to the phase detection module must meet the following two conditions:

[0043] ① Considering that the deviation of the measured value from the true value is bidirectional, it is necessary to ensure that the midpoint of the monotonic interval of the phase detection module's operating curve is exactly equal to the center frequency of the second bandpass filter 11. Therefore, when the output voltage of the phase detection module is 0.9 V, the frequency of the intermediate frequency signal generated after intermediate frequency conversion is 2.4 GHz, i.e., f IF =2.4 GHz;

[0044] ② To ensure that the measurement error of the frequency modulation light source measurement system does not exceed the measurement range R of the time delay phase detection frequency measurement system, given that the measurement error of the frequency modulation light source measurement system is within ±40 MHz, and considering that the voltage-phase difference curve of the phase detection module will exhibit periodic flips near -180° and 180°, the intermediate frequency signal frequency range R is set to 100 MHz, combined with f IF =2.4 GHz, set 2.35-2.45 GHz as the measurement range of the time delay phase detection frequency measurement system, which corresponds to the output voltage range of the phase detection module as 1.35-0.45 V.

[0045] To satisfy condition ①, f IF =2.4 GHz, V=0.9 V. Substituting these values ​​into the first piecewise function in formula (8), we obtain τ=104, 521, 937, 1354, 1772, 2189, 2606, 3023 ps, etc., and then substituting f... IF =2.4 GHz, V=0.9 V. Substituting these values ​​into the second piecewise function in formula (8), we can calculate τ=-104, -312, -729, -1145, -1563, -1981, -2397, -2815 ps, etc.

[0046] To satisfy condition ②, the relationship between the 2.35-2.45 GHz frequency range and the 1.35-0.45 V voltage range is established, and τ = 2500 ps is calculated. (Simultaneous conditions...) It is assumed that when τ = 2.6 ns, conditions ① and ② can be approximately satisfied simultaneously, at which point the time delay phase detection frequency measurement system can work normally. Therefore, the time delay of the tunable optical delay line is configured to 2.6 ns. Under this condition, the first signal generator 7 is set to output a linear sweep frequency with a frequency step of 2 MHz in the range of 2.35-2.45 GHz and sent to the second electro-optic modulator 14. The monotonically decreasing voltage distribution on the second analog-to-digital conversion module 19 is converted to a voltage-frequency correlation curve after time-frequency conversion. This curve is used as a reference to measure a series of microwave signals in the range of 2.35-2.45 GHz with a step of 2 MHz. Since the linear frequency modulated signal has a dwell time at each step frequency, the mean value of a series of voltages corresponding to each frequency value is calculated and compared with the frequency measurement reference curve for error analysis. The analysis shows that the maximum error at this time is less than 0.26 MHz. Figure 4 As shown, this device unifies a wide range of signals under test into a narrow bandwidth for precise measurement, achieving a significant optimization in accuracy from 40 MHz to 0.26 MHz.

Claims

1. A microwave frequency measurement device based on a frequency-modulated light source and time-delay phase detection, characterized in that, It includes a linear frequency modulated laser, a first electro-optic modulator, a 2×1 fiber coupler, a photodetector, a first bandpass filter, a first analog-to-digital converter module, a first signal generator, a second signal generator, an RF power divider, an RF mixer, a second bandpass filter, a continuous wave laser, a first 1×2 fiber coupler, a second electro-optic modulator, a second 1×2 fiber coupler, a tunable delay line, a dual-channel photodetector, a phase detection module, a second analog-to-digital converter module, and a feedback control module; The linear frequency modulated laser is connected to one input of a 2×1 fiber coupler. A first signal generator is connected to an RF power divider. One output of the RF power divider is connected to the RF port of a first electro-optic modulator. The optical output port of the first electro-optic modulator is connected to the other input of the 2×1 fiber coupler. The output of the 2×1 fiber coupler is connected to the input of a photodetector. The output of the photodetector is connected to the input of a first bandpass filter. The output of the first bandpass filter is connected to a first analog-to-digital converter module. The other output of the RF power divider is connected to one input of an RF mixer. A second signal generator is connected to the other input of the RF mixer. The output of the RF mixer is connected to the input of a second bandpass filter. The continuous wave laser is connected to the input of a first 1×2 fiber coupler. The first 1×2 fiber optic coupler has one output terminal connected to the optical input port of the first electro-optic modulator, and the other output terminal connected to the optical input port of the second electro-optic modulator. The output terminal of the second bandpass filter is connected to the radio frequency port of the second electro-optic modulator, and the optical output port of the second electro-optic modulator is connected to the input terminal of the second 1×2 fiber optic coupler. One output terminal of the second 1×2 fiber optic coupler is connected to the tunable optical delay line, which is connected to one optical input port of the dual-channel photodetector. The other output terminal of the second 1×2 fiber optic coupler is connected to the other optical input port of the dual-channel photodetector. The two output ports of the dual-channel photodetector are connected to the phase detection module, and the output terminal of the phase detection module is connected to the second analog-to-digital converter module. The result of the first analog-to-digital conversion module is sent to the feedback control module, which controls the frequency of the signal output from the local oscillator of the second signal generator, and the result of the second analog-to-digital conversion module is used as the output.

2. The microwave frequency measurement device based on frequency-modulated light source and time delay phase detection according to claim 1, characterized in that, The linear frequency modulated laser outputs frequency modulated continuous light. The output of the continuous wave laser is sent to the first electro-optic modulator via the first 1×2 fiber coupler. The test signal generated by the first signal generator is input to the RF port of the first electro-optic modulator after passing through the RF power divider. The bias voltage of the first electro-optic modulator is adjusted to make it work at the quadrature transmission point. The frequency sweep range of the linearly frequency-modulated laser is set to cover the carrier wave f of the output optical field of the first electro-optic modulator. c With the lower band f c -f e When the instantaneous frequency of the linearly frequency-modulated laser is different from the lower sideband f c -f e and carrier f c The beat frequency is equal to the center frequency f of the first bandpass filter. BPF At that time, the instantaneous frequency of the linearly frequency-modulated laser will be equal to f c -f e -f BPF f c -f e +f BPF f c -f BPF f c +f BPF Four pulses are generated at the corresponding time points. The first analog-to-digital conversion module calculates the interval Δt between the time points corresponding to the center points of the first two pulses and the time points corresponding to the center points of the last two pulses. Then, the frequency measurement value of the signal to be measured generated by the first signal generator is obtained. In the formula, γ represents the sweep rate of the linearly frequency-modulated laser.

3. The microwave frequency measurement device based on frequency-modulated light source and time delay phase detection according to claim 2, characterized in that, The frequency measurement value output by the first analog-to-digital converter module is sent to the feedback control module. The feedback control module controls the output frequency of the local oscillator signal from the second signal generator. f IF The preset ideal intermediate frequency; The true intermediate frequency after passing through the RF mixer and the second bandpass filter When the intermediate frequency signal is fed into the second electro-optic modulator, it modulates the carrier wave from the first 1×2 fiber coupler. The output light wave is then split into two paths after passing through the second 1×2 fiber coupler. One path is directly fed to one port of the dual-channel photodetector, and the other path is fed into the other port of the dual-channel photodetector after passing through an adjustable optical delay line. The two electrical signals output from the dual-channel photodetector enter the phase detection module, which identifies the phase difference between the two signals introduced by the adjustable optical delay line and forms a DC voltage output presented to the second analog-to-digital converter module. The actual intermediate frequency f is calculated based on the voltage value of the second analog-to-digital converter module. IF ʹ The output frequency measurement value .

4. The microwave frequency measurement device based on frequency-modulated light source and time delay phase detection according to claim 3, characterized in that, The actual intermediate frequency f is calculated based on the voltage value of the second analog-to-digital converter module. IF ʹ It is achieved based on the following formula: ； Where k and c are the operating parameters of the phase detection module itself, Δφ is the phase difference between the two signals entering the phase detection module, τ is the time delay between the two signals, and i is related to the phase detection period of the phase detection module, with values ​​of 1, 2, ...

5. The microwave frequency measurement device based on frequency-modulated light source and time delay phase detection according to claim 1, characterized in that, The measurement error of the frequency modulation light source frequency measurement system must be smaller than the measurement range of the time delay phase detection frequency measurement system.

6. The microwave frequency measurement device based on frequency-modulated light source and time delay phase detection according to claim 1, characterized in that, The midpoint of the monotonic interval of the phase detection module's operating curve is equal to the center frequency of the second bandpass filter.

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