Photonics-based flexible-tunable microwave signal frequency measurement device and method

Abstract

Disclosed is a photon technology-based flexible-tunable microwave signal frequency measurement device and method thereof; a sweeping local oscillator is modulated onto a first optical comb line of an optical frequency comb to obtain a scanning optical sideband; meanwhile, a tunable optical filter is used to select a specific optical comb line from other optical comb lines of the optical frequency comb, and a phase modulator is used to modulate a to-be-measured signal onto the selected optical comb line to obtain a to-be-measured signal optical sideband; after the scanning optical sideband and the to-be-measured signal optical sideband are balanced and detected, an electrical signal output by the balanced detection is filtered by a low-pass filter; and a signal acquisition and processing unit performs frequency-time mapping on the filtered electrical signal to obtain frequency information of the to-be-measured signal. The device and method thereof can realize flexible-tunable microwave signal frequency measurement, and can support flexible use of various frequency measurement tactics.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of microwave photonics and microwave signal processing, and particularly relates to a device and method for measuring the frequency of a flexibly tunable microwave signal based on photonics. BACKGROUND

[0002] Frequency measurement, as the core work of electromagnetic spectrum combat situation awareness, can detect the spectrum information in the electromagnetic environment and provide key reference for the next electronic attack and electronic protection decision. The traditional electrical technology cannot fully meet the performance requirements of frequency measurement technology in future electromagnetic warfare, such as high frequency, wide band and fast response. The two main problems are as follows: first, the electronic bottleneck of components limits the frequency (generally below 18 GHz), bandwidth (GHz level) and response speed (ms level) of signal processing, which cannot support the high-frequency wide-band and high-speed tuning frequency measurement capability; second, the high-frequency electronic system has large SWaP (size, weight and power consumption), which does not meet the development trend of miniaturized integrated equipment. Compared with the traditional electrical technology, microwave photonics technology has the advantages of ultra-wideband, high-speed response, low SWaP and anti-electromagnetic interference, which is expected to bring technical changes to electromagnetic warfare.

[0003] In recent years, researchers have conducted extensive research on frequency measurement schemes based on microwave photonics technology. The mainstream methods can be divided into three types: frequency-power mapping method, frequency-space mapping method and frequency-time mapping method. Among them, the frequency-power mapping method is only suitable for the measurement of single-frequency signals and cannot effectively cope with the complex electromagnetic environment in the battlefield; the frequency-space mapping method is based on the channelization idea to measure the instantaneous signal, and the measurement range, measurement resolution and system complexity are mutually restricted, which is difficult to balance the high-performance indicators and the development requirements of miniaturized integrated equipment; the frequency-time mapping method can build a mapping relationship between the frequency of the signal to be measured and the time of the output electrical pulse by scanning the frequency of the laser source, scanning the optical sideband and scanning the filter passband. This method has a relatively simple structure and high measurement accuracy, but the reported frequency-time mapping method generally focuses on the improvement of the measurement range, measurement resolution and measurement accuracy, and there is little research on high-speed flexible tuning of the measurement range, which cannot effectively support the flexible use of various frequency measurement tactics. SUMMARY

[0004] In order to overcome the shortcomings of the prior art, the application provides a device for measuring the frequency of a flexibly tunable microwave signal based on photonics, which comprises an optical frequency comb generator 1, an optical comb line separation structure 2, a single sideband modulator 3, a frequency-swept local oscillator 4, a tunable optical filter 5, a phase modulator 7, a balanced detector 9, a low-pass filter 10 and a signal acquisition and processing unit 11.

[0005] The optical frequency comb generator 1 outputs an optical frequency comb signal.

[0006] a light comb line separation structure 2, which receives the optical frequency comb signal output by the optical frequency comb generator 1, separates the optical frequency comb signal, and outputs a first optical comb line from a drop port and other optical comb lines from a pass port;

[0007] a sweep local oscillator 4, which outputs a sweep local oscillator signal;

[0008] a single sideband modulator 3, which receives the first optical comb line output by the light comb line separation structure 2 from the drop port, and outputs a scanning optical sideband;

[0009] a tunable optical filter 5, which receives the other optical comb lines output by the light comb line separation structure 2 from the pass port, and outputs a specific optical comb line;

[0010] a phase modulator 7, which receives the specific optical comb line output by the tunable optical filter 5, and outputs a to-be-measured signal optical sideband;

[0011] a balanced detector 9, which receives the scanning optical sideband output by the single sideband modulator 3 and the to-be-measured signal optical sideband output by the phase modulator 7, and outputs an electrical signal;

[0012] a low-pass filter 10, which filters the electrical signal output by the balanced detector 9, and outputs a filtered electrical signal;

[0013] a signal acquisition and processing unit 11, which receives the filtered electrical signal output by the low-pass filter 10, and completes frequency-time mapping processing.

[0014] In one specific embodiment of the present application, the light comb line separation structure 2 is composed of an optical circulator and a fiber Bragg grating (FBG).

[0015] In another specific embodiment of the present application, the light comb line separation structure 2 is composed of a micro-ring resonator in an up-down type.

[0016] In still another specific embodiment of the present application, the single sideband modulator 3 is implemented by using a double-drive Mach-Zehnder modulator (DDMZM).

[0017] In yet another specific embodiment of the present application, the tunable optical filter 5 is composed of a cascaded MZI structure or a micro-ring modulator in a straight-through type.

[0018] The working method of the above-mentioned flexible-tunable microwave signal frequency measurement device based on photon technology is as follows:

[0019] E(t) represents the optical frequency comb signal output by the optical frequency comb generator 1, wherein A represents the amplitude of all optical comb lines, f i i represents the frequency of the i-th optical comb line, Δf represents the comb tooth interval between the optical comb lines, and I represents the number of optical comb lines contained in the optical frequency comb, and then E(t) is represented as:

[0020]

[0021] wherein f1 represents the frequency of the first optical comb line;

[0022] After the optical frequency comb signal output by the optical frequency comb generator 1 passes through the optical comb line separation structure 2, the first optical comb line is dropped and modulated by the swept local oscillator 4 at the single sideband modulator 3 to obtain a swept optical sideband; the frequency of the swept local oscillator 4 is linearly scanned between 0 and Δf with T as the period, and the frequency of the swept local oscillator 4 is f l and the frequency of the swept optical sideband is f L respectively.

[0023]

[0024] Meanwhile, after the optical frequency comb signal passes through the optical comb line separation structure 2, the other optical comb lines are dropped and, after passing through the tunable optical filter 5, a certain specific optical comb line is selected out, assuming that the optical comb line is the i-th optical comb line, the frequency of the optical comb line is f i ; the specific optical comb line is modulated by the to-be-detected signal 8 at the subsequent phase modulator 7 to obtain a to-be-detected signal optical sideband; the frequency of the to-be-detected signal 8 is expressed as f s Under small signal modulation, the optical signal obtained after phase modulation contains -1 order optical sideband and +1 order optical sideband of the optical carrier with the frequency f i , the frequency of the -1 order optical sideband is f i -f s , and the frequency of the +1 order optical sideband is f i +f s ; since only the -1 order optical sideband can coincide with the frequency of the swept optical sideband, affecting the final frequency-time mapping, the frequency of the to-be-detected signal optical sideband is simplified as f S =f i -f s ;

[0025] The swept optical sideband and the to-be-detected signal optical sideband are input into the balanced detector 9 for photoelectric conversion; exp(j2πf L t) and exp(j2πf S t) are used to simply represent the swept optical sideband and the to-be-detected signal optical sideband respectively, and the output electrical signal is:

[0026]

[0027] Balanced detection can eliminate the self-beat components of the swept optical sideband and the to-be-detected signal optical sideband, and only keep the mutual beat components of the swept optical sideband and the to-be-detected signal optical sideband; after the electrical signal I PD output by the balanced detector 9 is filtered by the low-pass filter 10, the following is obtained:

[0028]

[0029] According to formula (4), when the signal acquisition and processing unit 11 detects an electrical pulse with a non-zero amplitude and measures its time t s After this, t s That is, the time t satisfying the equation t=(i-1-f s / Δf)T in formula (4), the frequency of the to-be-measured signal 8 is obtained by the following frequency-time mapping relationship:

[0030]

[0031] The obtained frequency measurement range is [(i-2)Δf, (i-1)Δf], and the selected specific optical comb line is switched by controlling the control signal 6 of the tunable optical filter 5, that is, the i is switched, so that the frequency measurement range can be tuned between [0, Δf], [Δf, 2Δf], [2Δf, 3Δf], … [(I-2)Δf, (I-1)Δf].

[0032] A flexible tunable microwave signal frequency measurement method based on photon technology is also provided, which is based on the above-mentioned flexible tunable microwave signal frequency measurement device based on photon technology, and includes the following steps:

[0033] Step 1: The first optical comb line and other optical comb lines output by the optical frequency comb generator 1 are separated by the optical comb line separation structure 2 and output in two paths;

[0034] Step 2: The first optical comb line transmitted by the optical comb line separation structure 2 is received by the single sideband modulator 3, and the sweep local oscillator signal output by the sweep local oscillator 4 is modulated onto the first optical comb line to obtain a scanning optical sideband and output; at the same time, the other optical comb lines transmitted by the optical comb line separation structure 2 are received by the tunable optical filter 5, and under the action of the control signal 6, a specific optical comb line is selected from the other optical comb lines and output; the specific optical comb line output by the tunable optical filter 5 is received by the phase modulator 7, and the to-be-measured signal 8 input from outside is modulated onto the specific optical comb line to obtain a to-be-measured signal optical sideband and output;

[0035] Step 3: The scanning optical sideband output by the single sideband modulator 3 and the to-be-measured signal optical sideband output by the phase modulator 7 are received by the balanced detector 9, and the two optical sideband signals are output as electrical signals after balanced detection; the electrical signals are filtered by the low-pass filter 10 and output;

[0036] Step 4: The filtered electrical signal output by the low-pass filter 10 is received by the signal acquisition and processing unit, and the frequency information of the to-be-measured signal 8 is obtained by frequency-time mapping.

[0037] The application utilizes the tunable optical filter to switch the selected optical frequency comb, can realize the frequency switching of the to-be-measured signal light sideband, and further complete the switching of the frequency measurement range. Therefore, by controlling the tunable optical filter, the flexible tuning of the frequency measurement range can be realized. The switching speed of the tunable optical filter in the application can reach the order of ns, which means that the frequency measurement range can realize the high-speed tuning of the order of ns. In addition, the use of the balanced detector just offsets the electrical signal component generated by the beat frequency of the to-be-measured signal light sideband, and can avoid the interference on the frequency measurement result. Finally, the application adopts the design of zero intermediate frequency reception, that is, a low-pass filter is connected at the rear end of the balanced detector, instead of the high-frequency band-pass filter used in the traditional high intermediate frequency reception, so that the image interference can be avoided, and the limitation of the traditional high intermediate frequency reception on the frequency measurement range and the frequency measurement resolution can be overcome. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 It is a structural schematic diagram of the flexible tunable microwave signal frequency measurement device of the application.

[0039] Figure 2 It is two implementation ways of the optical comb line separation structure. (a) Optical circulator combined with FBG; (b) upper download type micro-ring resonator.

[0040] Figure 3 It is a simulation scheme diagram of the flexible tunable microwave signal frequency measurement device.

[0041] Figure 4 It is the time domain diagram of the output electrical signal under two different settings, wherein Figure 4 (a) shows that the tunable optical filter is set to select the 4th optical comb line (corresponding to the frequency measurement range of 10-15GHz), and the to-be-measured signal contains two single frequency components of 13GHz and 11GHz; Figure 4 (b) shows that the tunable optical filter is set to select the 6th optical comb line (corresponding to the frequency measurement range of 20-25GHz), and the to-be-measured signal contains two single frequency components of 23GHz and 24GHz. DETAILED DESCRIPTION

[0042] The application will be described in detail below with reference to the drawings.

[0043] The application provides a flexible tunable microwave signal frequency measurement device based on photon technology, as shown in Figure 1 The device comprises an optical frequency comb generator (1), an optical comb line separation structure 2, a single sideband modulator 3, a frequency sweeping local oscillator 4, a tunable optical filter 5, a phase modulator 7, a balanced detector 9, a low-pass filter 10 and a signal acquisition and processing unit 11.

[0044] The optical frequency comb generator (1) outputs an optical frequency comb signal.

[0045] a light comb line separation structure 2, which receives the optical frequency comb signal output by the optical frequency comb generator 1, separates the optical frequency comb signal, and outputs a first optical comb line from a drop port and other optical comb lines from a pass port;

[0046] a sweep local oscillator 4, which outputs a sweep local oscillator signal;

[0047] a single sideband modulator 3, which receives the first optical comb line output by the light comb line separation structure 2 from the drop port, modulates the first optical comb line by the sweep local oscillator signal output by the sweep local oscillator 4, and outputs a swept optical sideband;

[0048] a tunable optical filter 5, which receives the other optical comb lines output by the light comb line separation structure 2 from the pass port, and selects a specific optical comb line under the control of an external control signal 6;

[0049] a phase modulator 7, which receives the specific optical comb line output by the tunable optical filter 5, and outputs a signal optical sideband under the modulation of an external signal to be measured 8.

[0050] a balanced photodetector 9, which receives the swept optical sideband output by the single sideband modulator 3 and the signal optical sideband output by the phase modulator 7, photoelectrically converts the two optical sidebands, and outputs an electrical signal, the frequency of the electrical signal being equal to the frequency difference between the swept optical sideband and the signal optical sideband;

[0051] a low-pass filter 10, which filters the electrical signal output by the balanced photodetector 9 and outputs a filtered electrical signal;

[0052] a signal acquisition and processing unit 11, which receives the filtered electrical signal output by the low-pass filter 10 and completes frequency-time mapping processing.

[0053] Preferably, the light comb line separation structure 2 can be composed of an optical circulator and an optical fiber Bragg grating (FBG) or only a micro-ring resonator of a downloading type, as shown in FIG. 1 and FIG. 2, respectively. Figure 2 The specific access modes of the two structures are well known to those skilled in the art and will not be described in detail. Figure 1

[0054] The single sideband modulator 3 can be implemented by a double-drive Mach-Zehnder modulator (DDMZM). The tunable optical filter 5 can be composed of a cascaded MZI structure (G. Wang, Q. Meng, Y. Li, et al. Results in Physics, 2023, 52(2): 106807.) or a micro-ring modulator of a straight-through type (F. Zhou, X. Wang, S. Yan, et al. IEEE Photonics Journal, 2018, 10(3): 7800809.), as shown in FIG. 3 and FIG. 4, respectively. Figure 1 ​The manner of implementation is well known to those skilled in the art and will not be elaborated here.

[0055] The theoretical process of the photon technology-based flexible-tunable microwave signal frequency measurement device is as follows:

[0056] E(t) represents the optical comb signal output by the optical comb generator 1, where A represents the amplitude of all the optical comb lines, f i represents the frequency of the i-th optical comb line, and Δf represents the comb tooth interval between the optical comb lines. If I represents the number of optical comb lines contained in the optical comb, then E(t) can be represented as:

[0057]

[0058] In the formula, f1 represents the frequency of the first optical comb line.

[0059] After the optical comb signal output by the optical comb generator 1 passes through the optical comb line separation structure 2, the first optical comb line is dropped and transmitted, and is modulated at the single-sideband modulator 3 by the swept local oscillator 4 to obtain a swept optical sideband. If the frequency of the swept local oscillator 4 is linearly scanned between 0 and Δf with a period of T, then the frequency f l of the swept local oscillator 4 and the frequency f L of the swept optical sideband can be represented as:

[0060]

[0061] Meanwhile, after the optical comb signal passes through the optical comb line separation structure 2, the other optical comb lines are transmitted upward, pass through the tunable optical filter 5, and are selected to be a certain specific optical comb line. Assuming that the optical comb line is the i-th optical comb line, then according to the foregoing definition, the frequency of the optical comb line is f i . The specific optical comb line is modulated by the to-be-measured signal 8 at the subsequent phase modulator 7 to obtain a to-be-measured signal optical sideband. If the frequency of the to-be-measured signal 8 is f s , under small-signal modulation, the optical signal obtained after phase modulation contains an optical carrier (with a frequency of f i ), a -1-order optical sideband (with a frequency of f i -f s ), and a +1-order optical sideband (with a frequency of f i +f s ). Since only the -1-order optical sideband can coincide with the frequency of the swept optical sideband, and thus affect the final frequency-time mapping, the frequency of the to-be-measured signal optical sideband can be simplified as f S =f i -f s .

[0062] The swept optical sideband and the to-be-measured signal optical sideband are input into the balanced detector 9 for photoelectric conversion. exp(j2πf Lt) and exp(j2πf S t) respectively represent the scanning light sideband and the to-be-detected signal light sideband, and the output electrical signal is:

[0063]

[0064] Obviously, the balanced detection can cancel the self-beat components of the scanning light sideband and the to-be-detected signal light sideband, and only keep the mutual-beat component of the scanning light sideband and the to-be-detected signal light sideband. The electrical signal I PD After filtering by the low-pass filter 10, the following can be obtained:

[0065]

[0066] According to formula (4), when the signal acquisition and processing unit 11 detects a non-zero-amplitude electrical pulse and measures the time t s t s that is, the time t satisfying the equation t = (i-1-f s / Δf)T in formula (4), the frequency of the to-be-detected signal 8 can be obtained according to the following frequency-time mapping relationship:

[0067]

[0068] It can be seen that the frequency measurement range is [(i-2)Δf, (i-1)Δf], and by controlling the control signal 6 of the tunable optical filter 5 to switch the selected specific optical comb line (that is, to switch i), the frequency measurement range can be tuned between [0, Δf], [Δf, 2Δf], [2Δf, 3Δf], … [(I-2)Δf, (I-1)Δf].

[0069] According to the same inventive idea, a flexible-tunable microwave signal frequency measurement method based on photon technology is also provided, including the following steps:

[0070] Step 1: The optical comb line separation structure 2 separates the first optical comb line and other optical comb lines output by the optical frequency comb generator 1, and outputs them in two paths.

[0071] Step 2: The single-sideband modulator 3 receives the first optical comb line transmitted by the optical comb line separation structure 2 in the lower path, modulates the sweep local oscillator signal output by the sweep local oscillator 4 onto the first optical comb line, obtains the scanning light sideband, and outputs it; at the same time, the tunable optical filter 5 receives the other optical comb lines transmitted by the optical comb line separation structure 2 in the upper path, selects a specific optical comb line from the other optical comb lines under the action of the control signal 6, and outputs it; the phase modulator 7 receives the specific optical comb line output by the tunable optical filter 5, modulates the externally input to-be-detected signal 8 onto the specific optical comb line, obtains the to-be-detected signal light sideband, and outputs it.

[0072] Step 3: The balanced detector 9 receives the scanning light sideband output by the single sideband modulator 3 and the signal light sideband output by the phase modulator 7, and outputs an electrical signal after balanced detection of the two optical sideband signals. The low-pass filter 10 filters the electrical signal and outputs.

[0073] Step 4: The signal acquisition and processing unit receives the filtered electrical signal output by the low-pass filter 10, performs frequency-time mapping on the signal, and obtains the frequency information of the signal to be measured.

[0074] In order to verify the effectiveness and feasibility of the application, a flexible tunable microwave signal frequency measurement is realized by combining with the simulation software Optisystem. In the simulation, the optical comb line separation structure is composed of an optical circulator and an FBG as shown in Figure 2 (a), the function of the single sideband modulator is completed by a DDMZM, the tunable optical filter is composed of a cascade MZI structure containing three MZIs, and the overall simulation scheme diagram is as shown in Figure 3 . The input optical frequency comb contains 8 optical comb lines, the starting frequency is 193 THz, and the optical comb line frequency interval is 5 GHz; the delay amounts of the three MZIs are set to 25 ps, 50 ps and 100 ps respectively; the frequency sweeping local oscillator is linearly swept from 0 GHz to 5 GHz, and the sweeping period is 10 μs; the FBG is set to just reflect the first optical comb line and transmit the remaining optical comb lines. Based on this, Figure 4 the time domain graphs of the output electrical signals under two different settings are given as follows:

[0075] 1. When the tunable optical filter is set to select the 4th optical comb line (corresponding to the frequency measurement range of 10-15 GHz), and the signal to be measured contains two single frequency components of 13 GHz and 11 GHz, the time domain graph of the output electrical signal is as shown in Figure 4 (a), it can be seen that there is an electrical pulse at 4 μs and 8 μs respectively, according to the frequency-time mapping relationship of formula (5), it can be deduced that the signal to be measured contains two single frequency components of 13 GHz and 11 GHz, and the simulation result conforms to the theoretical derivation.

[0076] 2. When the tunable optical filter is set to select the 6th optical comb line (corresponding to the frequency measurement range of 20-25 GHz), and the signal to be measured contains two single frequency components of 24 GHz and 23 GHz, the time domain graph of the output electrical signal is as shown in Figure 4 (b), it can be seen that there is a non-zero amplitude electrical output from 2 μs to 4 μs, according to the frequency-time mapping relationship of formula (5), it can be deduced that the signal to be measured contains two single frequency components of 24 GHz and 23 GHz, and the simulation result conforms to the theoretical derivation.

Claims

1. A flexibly tunable microwave signal frequency measurement device based on photonics technology, characterized in that, It includes an optical frequency comb generator (1), an optical comb line separation structure (2), a single-sideband modulator (3), a swept-frequency local oscillator (4), a tunable optical filter (5), a phase modulator (7), a balanced detector (9), a low-pass filter (10), and a signal acquisition and processing unit (11); among which Optical frequency comb generator (1), which outputs optical frequency comb signal; The optical comb line separation structure (2) receives the optical frequency comb signal output by the optical frequency comb generator (1), separates it, transmits the first optical comb line from the lower path, and transmits the other optical comb lines from the upper path. The local oscillator (4) is a frequency sweep oscillator, which outputs a frequency sweep oscillator signal; The single-sideband modulator (3) receives the first optical comb line output from the optical comb line separation structure (2) and outputs the scanning optical sideband. The tunable optical filter (5) receives other optical comb lines output from the optical comb line separation structure (2) and outputs a specific optical comb line. Phase modulator (7) receives a specific optical comb line output from tunable optical filter (5) and outputs the sideband of the signal light to be measured. The balanced detector (9) receives the scanning light sideband output by the single sideband modulator (3) and the test signal light sideband output by the phase modulator (7), and outputs an electrical signal. The low-pass filter (10) filters the electrical signal output by the balanced detector (9) and outputs a filtered electrical signal. The signal acquisition and processing unit (11) receives the filtered electrical signal output by the low-pass filter (10) and completes the frequency-time mapping process.

2. The flexibly tunable microwave signal frequency measurement device based on photonics technology as described in claim 1, characterized in that, The optical comb line separation structure (2) consists of an optical circulator and a fiber Bragg grating (FBG).

3. The photonics-based flexibly tunable microwave signal frequency measurement device as described in claim 1, characterized in that, The optical comb line separation structure (2) consists of an up-down micro-ring resonator.

4. The photonics-based flexibly tunable microwave signal frequency measurement device as described in claim 1, characterized in that, The single-sideband modulator (3) is implemented using a dual-drive Mach-Zehnder modulator (DDMZM).

5. The photonics-based flexibly tunable microwave signal frequency measurement device as described in claim 1, characterized in that, The tunable optical filter (5) consists of a cascaded MZI structure or a through-type micro-ring modulator.

6. The flexibly tunable microwave signal frequency measurement device based on photonics technology as described in any one of claims 1 to 5, its operation method is as follows: E(t) represents the optical frequency comb signal output by the optical frequency comb generator (1), where, Let A represent the amplitude of all optical comb lines, f i Let represent the frequency of the i-th optical comb line, Δf represent the tooth spacing between the optical comb lines, and I represent the number of optical comb lines contained in the optical frequency comb. Then E(t) can be expressed as: In the formula, f1 represents the frequency of the first optical comb line; The optical frequency comb signal output by the optical frequency comb generator (1) passes through the optical comb line separation structure (2), and the first optical comb line is transmitted from the lower path. It is modulated by the sweep local oscillator (4) at the single sideband modulator (3) to obtain the scanning optical sideband. Let the frequency of the sweep local oscillator (4) be linearly scanned between 0 and Δf with a period of T. Then the frequency f of the sweep local oscillator (4) is... l and the frequency f of the scanning optical sideband L They are represented as follows: Meanwhile, after the optical frequency comb signal passes through the optical comb line separation structure (2), other optical comb lines are transmitted from the upper path. After passing through the tunable optical filter (5), a specific optical comb line is selected. Assuming that the optical comb line is the i-th line, the frequency of the optical comb line is f. i The specific optical comb line is modulated by the signal under test (8) in the subsequent phase modulator (7) to obtain the optical sideband of the signal under test; the frequency of the signal under test (8) is expressed as f. s Under small-signal modulation, the optical signal obtained after phase modulation contains a frequency f. i The optical carrier has a -1st order optical sideband and a +1st order optical sideband, with the -1st order optical sideband frequency being f. i -f s The +1 order optical sideband frequency is f i +f s Since only the -1st order optical sideband may coincide with the scanning optical sideband frequency, affecting the final frequency-time mapping, the frequency of the optical sideband of the signal under test is simplified to f. S =f i -f s ; The scanning light sideband and the light sideband of the signal to be measured are input into the balanced detector (9) for photoelectric conversion; using exp(j2πf L t) and exp(j2πf S If we briefly represent the scanning optical sideband and the measured signal optical sideband respectively, then the output electrical signal is: The balanced detector can cancel out the beat frequency components of the scanning light sideband and the signal light sideband under test, retaining only the beat frequency components between the scanning light sideband and the signal light sideband under test; the electrical signal I output by the balanced detector (9) PD After filtering by low-pass filter (10), the following is obtained: According to formula (4), when the signal acquisition and processing unit (11) detects a non-zero amplitude electrical pulse and measures its time t s After that, the t here s That is, satisfying the equation t = (i-1-f) in formula (4). s At time t of / Δf)T, the frequency of the signal to be measured (8) is obtained from the following frequency-time mapping relationship: The obtained frequency measurement range is [(i-2)Δf, (i-1)Δf], and the selected specific optical comb line is switched by controlling the control signal (6) of the tunable optical filter (5), that is, switching i, so that the frequency measurement range can be tuned between [0,Δf], [Δf,2Δf], [2Δf,3Δf], ... [(i-2)Δf, (i-1)Δf].

7. A method for measuring the frequency of a flexibly tunable microwave signal based on photonics technology, wherein the method is based on the flexibly tunable microwave signal frequency measuring device based on photonics technology as described in any one of claims 1 to 5, characterized in that... Includes the following steps: Step 1: Use the optical comb line separation structure (2) to separate the first optical comb line output by the optical frequency comb generator (1) from the other optical comb lines and output them in two paths; Step 2: The single-sideband modulator (3) receives the first optical comb line transmitted from the optical comb line separation structure (2), modulates the sweep frequency local oscillator signal output by the sweep frequency local oscillator (4) onto the first optical comb line, obtains the scan optical sideband and outputs it; at the same time, the tunable optical filter (5) receives other optical comb lines transmitted from the optical comb line separation structure (2), and selects a specific optical comb line from the other optical comb lines for output under the action of the control signal (6); the phase modulator (7) receives a specific optical comb line output by the tunable optical filter (5), modulates the externally input test signal (8) onto the specific optical comb line, obtains the test signal optical sideband and outputs it; Step 3: The balanced detector (9) receives the scanning optical sideband output by the single-sideband modulator (3) and the signal optical sideband of the test output by the phase modulator (7). After the two optical sideband signals are balanced, they output electrical signals. The low-pass filter (10) filters the electrical signals and outputs them. Step 4: The signal acquisition and processing unit receives the filtered electrical signal output by the low-pass filter (10), performs frequency-time mapping on it, and obtains the frequency information of the signal under test.

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